Semiconductor laser apparatus, method of manufacturing semiconductor laser apparatus, and optical pickup apparatus

ABSTRACT

A monolithic red/infrared semiconductor laser device is joined to a blue-violet semiconductor laser device. The distance between a blue-violet emission point in the blue-violet semiconductor laser device and an infrared emission point in an infrared semiconductor laser device is significantly shorter than the distance between a red emission point in a red semiconductor laser device and the infrared emission point. A blue-violet laser beam, a red laser beam, and an infrared laser beam respectively emitted from the blue-violet emission point, the red emission point, and the infrared emission point are introduced into a photodetector after being incident on an optical disk by an optical system comprising a polarizing beam splitter, a collimator lens, a beam expander, a λ/4 plate, an objective lens, a cylindrical lens, and an optical axis correction element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor laser apparatus capableof emitting a plurality of light beams respectively having differentwavelengths, a method of manufacturing the semiconductor laserapparatus, and an optical pickup apparatus.

2. Description of the Background Art

Conventionally, semiconductor laser devices that emit infrared lightbeams having wavelengths of approximately 780 nm (infrared semiconductorlaser devices) have been used as light sources for compact disk (CD)drives. Further, semiconductor laser devices that emit red light beamshaving wavelengths of approximately 650 nm as light sources (redsemiconductor laser devices) have been used for conventional digitalversatile disk (DVD) drives.

On the other hand, DVDs capable of recording and reproduction usingblue-violet light beams having wavelengths of approximately 405 nm havebeen developed in recent years. In order to record and reproduce suchDVDs, DVD drives using semiconductor laser devices that emit blue-violetlight beams having wavelengths of approximately 405 nm (blue-violetsemiconductor laser devices) have been also simultaneously developed. Inthese DVD drives, compatibilities with conventional CDs and DVDs arerequired.

In this case, compatibility with conventional CDs, DVDs, and new DVDsare realized by methods of providing a plurality of optical pickupapparatuses that respectively emit infrared light beams, red lightbeams, and blue-violet light beams to DVD drives or methods of providinginfrared semiconductor laser devices, red semiconductor laser devices,and blue-violet semiconductor laser devices within one optical pickupapparatus. Since the number of components is increased in these methods,however, it is difficult to miniaturize the DVD drives, simplify theconfigurations, and reduce the costs.

In order to thus prevent the number of components from being increased,semiconductor laser devices in which infrared semiconductor laserdevices and red semiconductor laser devices are integrated into onechips have been put to practical use.

Both the infrared semiconductor laser devices and the red semiconductorlaser devices can be integrated into one chips because they are formedon GaAs substrates. On the other hand, the blue-violet semiconductorlaser devices are not formed on GaAs substrates, so that it issignificantly difficult to integrate both the blue-violet semiconductorlaser devices, together with the infrared semiconductor laser devicesand red semiconductor laser devices, into one chips.

Therefore, a light emitting apparatus having a configuration in which aninfrared semiconductor laser device and a red semiconductor laser deviceare formed on the same chip to manufacture a monolithic red/infraredsemiconductor laser device, a blue-violet semiconductor laser device isformed into separate chips, and the chips of the blue-violetsemiconductor laser device and the chips of the monolithic red/infraredsemiconductor laser device are stacked has been proposed (see JP2001-230502 A, for example).

In a case where the light emitting apparatus is mounted within anoptical pickup apparatus, spaces respectively occupied by theblue-violet semiconductor laser device, the infrared semiconductor laserdevice, and the red semiconductor laser device in the optical pickupapparatus are reduced.

In the above-mentioned light emitting apparatus, respective emissionpoints of the semiconductor laser devices are spaced apart from oneanother. Consequently, it is preferable that the optical pickupapparatus containing the plurality of semiconductor laser devices isprovided with an optical system and a photodetector corresponding toeach of the semiconductor laser devices. In this case, it is possible toaccurately introduce light beams emitted from the plurality ofsemiconductor laser devices into the optical recording medium as well asto accurately introduce light beams reflected from the optical recordingmedium into the photodetector. When the optical pickup apparatus isprovided with the optical system and the photodetector corresponding toeach of the semiconductor laser devices, however, the size of theoptical pickup apparatus is increased.

In JP 2001-230502 A, an example in which a light emitting devicecomprising a blue-violet semiconductor laser device, an infraredsemiconductor laser device, and a red semiconductor laser device ismounted within an optical disk recording/reproducing device providedwith an optical system and a photodetector that are common among thethree semiconductor laser devices is illustrated.

However, optical paths of laser beams respectively emitted from theblue-violet semiconductor laser device, the red semiconductor laserdevice, and the infrared semiconductor laser device do not coincide withone another. In order to carry out accurate signal reproduction,tracking control, focus control, and tilt control, therefore, an opticaldisk recording/reproducing apparatus must be actually provided withthree photodetectors corresponding to three laser beams. Consequently,it is difficult to miniaturize the optical disk recording/reproducingapparatus.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a semiconductor laserapparatus capable of miniaturizing an optical pickup apparatus, and amethod of manufacturing the same.

Another object of the present invention is to provide an optical pickupapparatus that can be miniaturized.

(1)

A semiconductor laser apparatus according to an aspect of the presentinvention comprises a first semiconductor laser device, a secondsemiconductor laser device, and a third semiconductor laser device, thefirst semiconductor laser device comprising a first semiconductor layerhaving a first emission point emitting a light beam having a firstwavelength in a direction substantially parallel to a first direction ona first substrate, the second semiconductor laser device comprising asecond semiconductor layer having a second emission point emitting alight beam having a second wavelength different from a natural numbertimes the first wavelength in the direction substantially parallel tothe first direction, the third semiconductor laser device comprising athird semiconductor layer having a third emission point emitting a lightbeam having a third wavelength substantially equal to a natural numbertimes the first wavelength in the direction substantially parallel tothe first direction, the second semiconductor laser device and the thirdsemiconductor laser device being stacked on the first semiconductorlaser device such that the second semiconductor layer and the thirdsemiconductor layer are opposed to the first semiconductor layer, andthe distance between the first emission point and the third emissionpoint being shorter than the distance between the first emission pointand the second emission point on a first plane perpendicular to thefirst direction.

In the semiconductor laser apparatus, the light beam having the firstwavelength is emitted in the direction substantially parallel to thefirst direction from the first emission point in the first semiconductorlaser device, the light beam having the second wavelength different fromthe natural number times the first wavelength is emitted in thedirection substantially parallel to the first direction from the secondemission point in the second semiconductor laser device, and the lightbeam having the third wavelength substantially equal to the naturalnumber times the first wavelength is emitted in the directionsubstantially parallel to the first direction from the third emissionpoint in the third semiconductor laser device.

Here, the second semiconductor laser device and the third semiconductorlaser device are stacked on the first semiconductor laser device suchthat the second semiconductor layer and the third semiconductor layerare opposed to the first semiconductor layer, and the distance betweenthe first emission point and the third emission point is shorter thanthe distance between the first emission point and the second emissionpoint on the first plane perpendicular to the first direction. Thus, inthe direction perpendicular to the one surface of the first substrate,the first emission point and the third emission point are in closeproximity to each other.

Since the third wavelength is substantially equal to the natural numbertimes the first wavelength, a diffraction efficiency in a case where thelight beam having the first wavelength is incident on a diffractiongrating and a diffraction efficiency in a case where the light beamhaving the third wavelength is incident on the diffraction grating cansubstantially be equalized. Then, because the second wavelength differsfrom the natural number times the first wavelength, a diffractionefficiency in a case where the light beam having the first wavelength isincident on a diffraction grating and a diffraction efficiency in a casewhere the light beam having the second wavelength is incident on adiffraction grating differ from each other. Therefore, when afirst-order diffracted light beam of the second semiconductor laser beamis enhanced, zeroth-order diffracted light beams of the firstsemiconductor laser beam and the third semiconductor laser beam cansimultaneously be enhanced by adjustment of height of the diffractiongrating.

Thus, the zeroth-order diffracted light beams respectively having thefirst and third wavelength and the first-order diffracted light beamshaving the second wavelength can be introduced into a photodetector bybeing incident on the diffraction grating.

Consequently, the light beams respectively having the first, second, andthird wavelengths can be received by the one photodetector.

As a result, an arrangement space of the photodetector in the opticalpickup apparatus can be reduced, which allows the optical pickupapparatus to be miniaturized.

(2)

The first and third emission points may be arranged along a directionsubstantially perpendicular to one surface of the first substrate. Thus,the distance between the first emission point and the third emissionpoint is reduced to a minimum.

(3)

The first semiconductor layer may comprise a first cavity extending inthe direction substantially parallel to the first direction, the secondsemiconductor layer may comprise a second cavity extending in thedirection substantially parallel to the first direction, the thirdsemiconductor layer may comprise a third cavity extending in thedirection substantially parallel to the first direction, and at leastone of the length of the second cavity and the length of the thirdcavity may be larger than the length of the first cavity.

In this case, at least one of the length of the second cavity and thelength of the third cavity is larger than the length of the firstcavity, so that there occurs a portion where the first semiconductorlayer is not joined to the vicinity of a facet of at least one of thesecond cavity and the third cavity. Thus, distortion on the facet of atleast one of the second and third cavities is reduced. Consequently,degradation of at least one of the second and third semiconductor laserdevices is restrained, resulting in improved reliability.

(4)

The first semiconductor laser device may further comprise a firstelectrode formed on the first semiconductor layer, the secondsemiconductor laser device may further comprise a second electrodeformed on the second semiconductor layer, the third semiconductor laserdevice may further comprise a third electrode formed on the thirdsemiconductor layer, and the first electrode, the second electrode, andthe third electrode may be insulated from one another.

Thus, arbitrary voltages can be respectively applied to the first,second, and third electrodes. Consequently, a system for driving thefirst, second, and third semiconductor laser devices can be arbitrarilyselected.

(5)

The second semiconductor laser device may further comprise a secondsubstrate, the second semiconductor layer being formed on the secondsubstrate, the third semiconductor laser device may further comprise athird substrate, the third semiconductor layer being formed on the thirdsubstrate, and at least one of the second substrate and the thirdsubstrate may be composed of a material different from the firstsubstrate.

In this case, the semiconductor laser apparatus comprising thesubstrates composed of the different materials is integrally formed.

(6)

The second and third substrates may be a common substrate, and thesecond semiconductor layer may be formed in a first region of the commonsubstrate, and the third semiconductor layer may be formed in a secondregion of the common substrate.

In this case, the second semiconductor laser device and the thirdsemiconductor laser device are integrated with the common substrate, sothat the second and third emission points are easy to position withrespect to the first emission point.

(7)

A thickness from the common substrate to a surface of the secondsemiconductor layer may be larger than a thickness from the commonsubstrate to a surface of the third semiconductor layer in a directionsubstantially perpendicular to one surface of the first substrate.

In this case, the first substrate and the second substrate are stackedsubstantially parallel to each other. Thus, the second and thirdsemiconductor laser devices can be stably provided on the firstsemiconductor laser device, and the second and third semiconductor laserdevices can be reliably joined to the first semiconductor laser device.

(8)

The surface of the second semiconductor layer may project toward thefirst substrate farther than the surface of the third semiconductorlayer in the direction substantially perpendicular to one surface of thefirst substrate.

In this case, the first substrate and the second substrate are stackedsubstantially parallel to each other. Thus, the second and thirdsemiconductor laser devices can be stably provided on the firstsemiconductor laser device, and the second and third semiconductor laserdevices can be reliably joined to the first semiconductor laser device.

(9)

The first semiconductor layer may comprise a first projection extendingin the direction substantially parallel to the first direction, thethird semiconductor layer may comprise a third projection extending inthe direction substantially parallel to the first direction, and thewidth of the third projection may be larger than the width of the firstprojection in a second direction perpendicular to the first directionand parallel to one surface of the first substrate. In this case, thewidth of the third projection is large, so that the third projection canbe stably arranged on the first projection. Further, the thirdprojection is prevented from applying a local stress to the firstprojection. Thus, the first semiconductor layer is prevented from beingdegraded.

(10)

The second semiconductor layer may comprise a second projectionextending in the direction substantially parallel to the firstdirection, and the width of the third projection may be larger than thewidth of the second projection in the second direction. In this case,the width of the third projection is large, so that the third projectioncan be stably arranged on the first projection. Further, the thirdprojection is prevented from applying a local stress to the firstprojection. Thus, the first semiconductor layer is prevented from beingdegraded. At this time, the second projection does not come into contactwith the first projection, so that the second projection does not applya local stress to the first projection.

(11)

The semiconductor laser apparatus may further comprise a packageaccommodating the first semiconductor laser device, the secondsemiconductor laser device, and the third semiconductor laser device aswell as having a light extraction window, and the first semiconductorlaser device may be arranged such that a light beam having a firstwavelength emitted from the first emission point in the firstsemiconductor laser device passes through a substantially centralportion of the extraction window.

In this case, even if the package is rotated around the central axis ofthe package, the change in the axis of the laser beam emitted from thefirst semiconductor laser device can be reduced. Even when the intensityof the light beam having the first wavelength is weaker than therespective intensities of the light beams having the second and thirdwavelengths, therefore, the respective angles of an optical systemcomprising lens etc. and the package can be easily adjusted with respectto the central axis of the package while increasing the light extractionefficiency of the first semiconductor laser device. As a result, theoptical system is easy to design.

(12)

The light beam having the first wavelength may be a blue-violet lightbeam, the light beam having the second wavelength may be a red lightbeam, and the light beam having the third wavelength may be an infraredlight beam. In this case, the light beams respectively having aplurality of colors (wavelength) can be emitted from the onesemiconductor laser apparatus.

(13)

The first semiconductor layer may be composed of a nitride basedsemiconductor. In this case, the first semiconductor laser device canemit the blue-violet light beam.

(14)

The second semiconductor layer may be composed of a gallium indiumphosphide based semiconductor. In this case, the second semiconductorlaser device can emit the red light beam.

(15)

The third semiconductor layer may be composed of a gallium arsenidebased semiconductor. In this case, the third semiconductor laser devicecan emit the infrared light beam.

(16)

An optical pickup apparatus according to another aspect of the presentinvention is an optical pickup apparatus that irradiates a light beamonto an optical recording medium and detects the light beam returnedfrom the optical recording medium, comprising a semiconductor laserapparatus, the semiconductor laser apparatus comprising a firstsemiconductor laser device, a second semiconductor laser device, and athird semiconductor laser device, the first semiconductor laser devicecomprising a first semiconductor layer having a first emission pointemitting a light beam having a first wavelength in a directionsubstantially parallel to a first direction on a first substrate, thesecond semiconductor laser device comprising a second semiconductorlayer having a second emission point emitting a light beam having asecond wavelength different from a natural number times the firstwavelength in the direction substantially parallel to the firstdirection, the third semiconductor laser device comprising a thirdsemiconductor layer having a third emission point emitting a light beamhaving a third wavelength substantially equal to a natural number timesthe first wavelength in the direction substantially parallel to thefirst direction, the second semiconductor laser device and the thirdsemiconductor laser device being stacked on the first semiconductorlaser device such that the second semiconductor layer and the thirdsemiconductor layer are opposed to the first semiconductor layer, andthe distance between the first emission point and the third emissionpoint being shorter than the distance between the first emission pointand the second emission point on a first plane perpendicular to thefirst direction.

In the optical pickup apparatus, the light beam having the first,second, or third wavelength is selectively emitted from thesemiconductor laser apparatus. Here, the semiconductor laser apparatusallows the light beams respectively having the first, second, and thirdwavelengths to be introduced into one photodetector. Consequently, aplurality of photodetectors need not be provided in the optical pickupapparatus. As a result, an arrangement space of the photodetector in theoptical pickup apparatus can be reduced, which allows the optical pickupapparatus to be miniaturized.

(17)

The optical pickup apparatus may further comprise a photodetector, andan optical system that introduces the light beam having the first,second, or third wavelength emitted from the semiconductor laserapparatus to the optical recording medium and introduces the light beamhaving the first, second, or third wavelength returned from the opticalrecording medium to the photodetector.

In this case, the light beams respectively having the first, second, andthird wavelengths returned from the optical recording medium areintroduced into the one photodetector. Thus, an arrangement space of thephotodetector in the optical pickup apparatus can be reduced, whichallows the optical pickup apparatus to be miniaturized.

(18)

The optical system comprises a diffraction grating that transmits thelight beams respectively having the first, second, and third wavelengthssuch that the light beams having the first, second, and thirdwavelengths are introduced into the photodetector.

In this case, the light beam having the first wavelength emitted fromthe semiconductor laser apparatus is introduced into the opticalrecording medium by the optical system, and is returned from the opticalrecording medium and introduced into the photodetector. The light beamhaving the second wavelength emitted from the semiconductor laserapparatus is introduced into the optical recording medium by the opticalsystem, and is returned from the optical recording medium and introducedinto the photodetector. Further, the light beam having the thirdwavelength emitted from the semiconductor laser apparatus is introducedinto the optical recording medium by the optical system, and is returnedfrom the optical recording medium and introduced into the photodetector.

Here, in the semiconductor laser apparatus, the second semiconductorlaser device and the third semiconductor laser device are stacked on thefirst semiconductor laser device such that the second semiconductorlayer and the third semiconductor layer are opposed to the firstsemiconductor layer, and the distance between the first emission pointand the third emission point is shorter than the distance between thefirst emission point and the second emission point on the first planeperpendicular to the first direction. In the direction perpendicular tothe one surface of the first substrate, therefore, the first emissionpoint and the third emission point are in close proximity to each other.

Since the third wavelength is substantially equal to the natural numbertimes the first wavelength, a diffraction efficiency in a case where thelight beam having the first wavelength is incident on a diffractiongrating and a diffraction efficiency in a case where the light beamhaving the third wavelength is incident on the diffraction grating cansubstantially be equalized. Then, because the second wavelength differsfrom the natural number times the first wavelength, a diffractionefficiency in a case where the light beam having the first wavelength isincident on a diffraction grating and a diffraction efficiency in a casewhere the light beam having the second wavelength is incident on adiffraction grating differ from each other. Therefore, when afirst-order diffracted light beam of the second semiconductor laser beamis enhanced, zeroth-order diffracted light beams of the firstsemiconductor laser beam and the third semiconductor laser beam cansimultaneously be enhanced by adjustment of height of the diffractiongrating.

Thus, the zeroth-order diffracted light beams respectively having thefirst and third wavelength and the first-order diffracted light beamshaving the second wavelength can be introduced into a photodetector bybeing incident on the diffraction grating.

Consequently, the light beams respectively having the first, second, andthird wavelengths can be received by the one photodetector.

As a result, an arrangement space of the photodetector in the opticalpickup apparatus can be reduced, which allows the optical pickupapparatus to be miniaturized.

(19)

A method of manufacturing a semiconductor laser apparatus according tostill another aspect of the present invention comprises the steps offorming a first semiconductor layer having a first emission pointemitting a light beam having a first wavelength in a directionsubstantially parallel to a first direction on a first substrate,forming a second semiconductor layer having a second emission pointemitting a light beam having a second wavelength different from anatural number times the first wavelength in the direction substantiallyparallel to the first direction on a second substrate and a thirdsemiconductor layer having a third emission point emitting a light beamhaving a third wavelength substantially equal to a natural number timesthe first wavelength in the direction substantially parallel to thefirst direction; and affixing one surface of the second semiconductorlayer to one surface of the first semiconductor layer such that thedistance between the first emission point and the third emission pointis shorter than the distance between the first emission point and thesecond emission point on a first plane perpendicular to the firstdirection.

In the semiconductor laser apparatus manufactured by the manufacturingmethod, the light beam having the first wavelength is emitted in thedirection substantially parallel to the first direction from the firstemission point in the first semiconductor laser device, the light beamhaving the second wavelength different from the natural number times thefirst wavelength is emitted in the direction substantially parallel tothe first direction from the second emission point in the secondsemiconductor laser device, and the light beam having the thirdwavelength substantially equal to the natural number times the firstwavelength is emitted in the direction substantially parallel to thefirst direction from the third emission point in the third semiconductorlaser device.

Here, on the first plane perpendicular to the first direction, the onesurface of the second semiconductor layer on the second substrate isaffixed to the one surface of the first semiconductor layer on the firstsubstrate such that the distance between the first emission point andthe third emission point is shorter than the distance between the firstemission point and the second emission point. In the directionperpendicular to the one surface of the first substrate, therefore, thefirst emission point and the third emission point are in close proximityto each other.

Since the third wavelength is substantially equal to the natural numbertimes the first wavelength, a diffraction efficiency in a case where thelight beam having the first wavelength is incident on a diffractiongrating and a diffraction efficiency in a case where the light beamhaving the third wavelength is incident on the diffraction grating cansubstantially be equalized. Then, because the second wavelength differsfrom the natural number times the first wavelength, a diffractionefficiency in a case where the light beam having the first wavelength isincident on a diffraction grating and a diffraction efficiency in a casewhere the light beam having the second wavelength is incident on adiffraction grating differ from each other. Therefore, when afirst-order diffracted light beam of the second semiconductor laser beamis enhanced, zeroth-order diffracted light beams of the firstsemiconductor laser beam and the third semiconductor laser beam cansimultaneously be enhanced by adjustment of height of the diffractiongrating.

Thus, the zeroth-order diffracted light beams respectively having thefirst and third wavelength and the first-order diffracted light beamshaving the second wavelength can be introduced into a photodetector bybeing incident on the diffraction grating.

Consequently, the light beams respectively having the first, second, andthird wavelengths can be received by the one photodetector.

As a result, an arrangement space of the photodetector in the opticalpickup apparatus can be reduced, which allows the optical pickupapparatus to be miniaturized.

The second semiconductor laser device and the third semiconductor laserdevice are integrated by the second substrate, so that the second andthird emission points are easy to position with respect to the firstemission point.

(20)

The thickness of the second semiconductor layer may be larger than thethickness of the third semiconductor layer in a direction substantiallyperpendicular to one surface of the first substrate.

In this case, the first substrate and the second substrate are stackedsubstantially parallel to each other. Thus, the second and thirdsemiconductor laser devices can be stably provided on the firstsemiconductor laser device, and the second and third semiconductor laserdevices can be reliably joined to the first semiconductor laser device.

(21)

The surface of the second semiconductor layer may project toward thefirst substrate farther than a surface of the third semiconductor layerin the direction substantially perpendicular to one surface of the firstsubstrate.

In this case, the first substrate and the second substrate are stackedsubstantially parallel to each other. Thus, the second and thirdsemiconductor laser devices can be stably provided on the firstsemiconductor laser device, and the second and third semiconductor laserdevices can be reliably joined to the first semiconductor laser device.

Other features, elements, characteristics, and advantages of the presentinvention will become more apparent from the following description ofpreferred embodiments of the present invention with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view showing an example of a semiconductor laserapparatus according to a first embodiment;

FIG. 2 is a cross-sectional view taken along a line A1-A1 shown in FIG.1;

FIG. 3 is a schematic view of a junction plane of a blue-violetsemiconductor laser device, a red semiconductor laser device, and aninfrared semiconductor laser device in a semiconductor laser apparatus;

FIG. 4 is a schematic view of a junction plane of a blue-violetsemiconductor laser device, a red semiconductor laser device, and aninfrared semiconductor laser device in a semiconductor laser apparatus;

FIG. 5 is a perspective view showing the appearance of a substantiallyround-shaped can package for laser devices on which the semiconductorlaser apparatus shown in FIG. 1 is mounted;

FIG. 6 is a schematic front view showing a state where a cover in thesubstantially round-shaped can package for laser devices shown in FIG. 5is removed;

FIG. 7 is a schematic top view showing a state where a cover in thesubstantially round-shaped can package for laser devices shown in FIG. 5is removed;

FIG. 8 is a schematic sectional view showing the steps of an example ofa method of manufacturing the semiconductor laser apparatus according tothe first embodiment;

FIG. 9 is a schematic sectional view showing the steps of an example ofa method of manufacturing the semiconductor laser apparatus according tothe first embodiment;

FIG. 10 is a schematic sectional view showing the steps of an example ofa method of manufacturing the semiconductor laser apparatus according tothe first embodiment;

FIG. 11 is a schematic sectional view showing the steps of an example ofa method of manufacturing the semiconductor laser apparatus according tothe first embodiment;

FIG. 12 is a schematic sectional view for explaining the details of theconfiguration of a blue-violet semiconductor laser device;

FIG. 13 is a schematic sectional view for explaining the details of theconfiguration of a red semiconductor laser device in a monolithicred/infrared semiconductor laser device;

FIG. 14 is a schematic sectional view for explaining the details of theconfiguration of an infrared semiconductor laser device in a monolithicred/infrared semiconductor laser device;

FIG. 15 is a diagram showing the configuration of an optical pickupapparatus;

FIG. 16 is a diagram showing another example of the configuration of anoptical pickup apparatus;

FIG. 17 is a diagram showing still another example of the configurationof an optical pickup apparatus;

FIG. 18 is a diagram for explaining the function of connecting theoptical axis of a parallel plate in the optical pickup apparatus shownin FIG. 17;

FIG. 19 is a diagram for explaining a preferred inclination angle θ of aparallel plate;

FIG. 20 is a diagram showing still another example of the configurationof an optical pickup apparatus;

FIG. 21 is a schematic top view for explaining the configuration of asemiconductor laser apparatus according to a second embodiment;

FIG. 22 is a top view showing an example of a semiconductor laserapparatus according to a third embodiment;

FIG. 23 is a schematic view of a junction plane of a blue-violetsemiconductor laser device and a monolithic red/infrared semiconductorlaser device in the semiconductor laser apparatus shown in FIG. 22;

FIG. 24 is a schematic view of a junction plane of a blue-violetsemiconductor laser device and a monolithic red/infrared semiconductorlaser device in the semiconductor laser apparatus shown in FIG. 22;

FIG. 25 is a schematic front view showing a state where thesemiconductor laser apparatus shown in FIG. 22 is mounted within thesubstantially round-shaped can package for laser devices shown in FIG. 5to remove the cover;

FIG. 26 is a schematic top view showing a state where the semiconductorlaser apparatus shown in FIG. 22 is mounted within the substantiallyround-shaped can package for laser devices shown in FIG. 5 to remove thecover;

FIG. 27 is a top view showing an example of a semiconductor laserapparatus according to a fourth embodiment;

FIG. 28 is a cross-sectional view taken along a line A3-A3 shown in FIG.27;

FIG. 29 is a schematic view of a junction plane of a blue-violetsemiconductor laser device, a red semiconductor laser device, and aninfrared semiconductor laser device in a semiconductor laser apparatus;

FIG. 30 is a schematic view of a junction plane of a blue-violetsemiconductor laser device, a red semiconductor laser device, and aninfrared semiconductor laser device in a semiconductor laser apparatus;

FIG. 31 is a schematic front view showing a state where thesemiconductor laser apparatus shown in FIGS. 27 and 28 is mounted withinthe substantially round-shaped can package for laser devices shown inFIG. 5 to remove the cover;

FIG. 32 is a top view showing an example of a semiconductor laserapparatus according to a fifth embodiment;

FIG. 33 is a cross-sectional view taken along a line A4-A4 shown in FIG.32; and

FIG. 34 is a schematic front view showing a state where thesemiconductor laser apparatus shown in FIGS. 32 and 33 is mounted withinthe substantially round-shaped can package for laser devices shown inFIG. 5 to remove the cover.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A semiconductor laser apparatus according to an embodiment of thepresent invention and an optical pickup apparatus comprising the samewill be described.

(1) First Embodiment

A semiconductor laser apparatus according to a first embodiment of thepresent invention comprises a semiconductor laser device emitting alaser beam having a wavelength of approximately 405 nm (hereinafterreferred to as a blue-violet semiconductor laser device), asemiconductor laser device emitting a laser beam having a wavelength ofapproximately 650 nm (hereinafter referred to as a red semiconductorlaser device), and a semiconductor laser device emitting a laser beamhaving a wavelength of approximately 780 nm (hereinafter referred to asan infrared semiconductor laser device).

(a) Configuration of Semiconductor Laser Apparatus

FIGS. 1 and 2 are schematic views for explaining the configuration of asemiconductor laser apparatus according to a first embodiment. FIG. 1 isa top view showing an example of the semiconductor laser apparatusaccording to the first embodiment, and FIG. 2 is a cross-sectional viewtaken along a line A1-A1 shown in FIG. 1. FIGS. 3 and 4 are schematicviews of a junction plane of the blue-violet semiconductor laser device,the red semiconductor laser device, and the infrared semiconductor laserdevice in the semiconductor laser apparatus shown in FIGS. 1 and 2.

In FIGS. 1, 2, 3, and 4, three directions that are perpendicular to oneanother, as indicated by arrows X, Y, and Z, are respectively taken asan X-direction, a Y-direction, and a Z-direction. The X-direction andthe Y-direction are directions parallel to respective p-n junctioninterfaces 10, 20, and 30 of the blue-violet semiconductor laser device1, the red semiconductor laser device 2, and the infrared semiconductorlaser device 3, described later. The Z-direction is a directionperpendicular to the respective p-n junction interfaces 10, 20, and 30of the blue-violet semiconductor laser device 1, the red semiconductorlaser device 2, and the infrared semiconductor laser device 3.

As shown in FIGS. 1 and 2, a striped projection T1 extending in theX-direction is formed on an upper surface of the blue-violetsemiconductor laser device 1. The projection T1 is positioned in an areaoffset from the center of the blue-violet semiconductor laser device 1in the Y-direction. An insulating film 4 a is formed so as to cover theupper surface of the blue-violet semiconductor laser device 1 on a sidesurface of the projection T1 and on both sides of the projection T1. Ap-type ohmic electrode 621 is formed on an upper surface of theprojection T1.

A p-side pad electrode 12 is formed so as to cover an upper surface ofthe p-type ohmic electrode 621 and the insulating film 4 a in thevicinity of the projection T1. An n-electrode 15 is formed on a lowersurface of the blue-violet semiconductor laser device 1. A p-n junctioninterface 10 serving as a junction interface of a p-type semiconductorand an n-type semiconductor is formed in the blue-violet semiconductorlaser device 1.

In the present embodiment, the red semiconductor laser device 2 and theinfrared semiconductor laser device 3 are integrally formed. The redsemiconductor laser device 2 and the infrared semiconductor laser device3 that are integrally formed are referred to as a monolithicred/infrared semiconductor laser device 23X.

In the monolithic red/infrared semiconductor laser device 23X, the redsemiconductor laser device 2 and the infrared semiconductor laser device3 are formed on a common substrate. The details will be described later.

A common n-electrode 233 is formed on respective upper surfaces of thered semiconductor laser device 2 and the infrared semiconductor laserdevice 3. A striped projection T2 extending in the X-direction is formedon a lower surface of the red semiconductor laser device 2. A p-side padelectrode 22 is formed on the lower surface of the red semiconductorlaser device 2. The p-n junction interface 20 serving as a junctioninterface of a p-type semiconductor and an n-type semiconductor isformed in the red semiconductor laser device 2.

A striped projection T3 extending in the X-direction is formed on theside of a lower surface of the infrared semiconductor laser device 3. Ap-side pad electrode 32 is formed on the lower surface of the infraredsemiconductor laser device 3. The p-n junction interface 30 serving as ajunction interface of a p-type semiconductor and an n-type semiconductoris formed in the infrared semiconductor laser device 3.

In the present embodiment, the length in the Z-direction of the redsemiconductor laser device 2 is 1 μm larger than the length in theZ-direction of the infrared semiconductor laser device 3. A surface of asemiconductor layer on the side of the lower surface of the projectionT2 in the red semiconductor laser device 2 projects toward theblue-violet semiconductor laser device 1 in the Z-direction 1 μm fartherthan a surface of a semiconductor layer on the side of the lower surfaceof the projection T3 in the infrared semiconductor laser device 3. Thesemiconductor layer will be described later. P-type ohmic electrodes arealso respectively formed on the projections T2 and T3 (not shown in FIG.2).

The monolithic red/infrared semiconductor laser device 23X is joined tothe blue-violet semiconductor laser device 1 such that the projection T3and the projection T1 are opposed to each other on a substantiallystraight line in the Z-direction.

A junction of the blue-violet semiconductor laser device 1 and themonolithic red/infrared semiconductor laser device 23X will be thendescribed.

As shown in FIG. 3 (a), the p-side pad electrode 12 and the p-side padelectrode 13, described above, are formed on the insulating film 4 a inthe blue-violet semiconductor laser device 1.

The p-side pad electrode 12 extends in the X-direction along theprojection T1 in the blue-violet semiconductor laser device 1, and itspart extends in the Y-direction.

The p-side pad electrode 13 extends in the X-direction at a positionspaced apart from the p-side pad electrode 12, and its part extends in adirection opposite to the p-side pad electrode 12.

The p-side pad electrodes 12 and 13 are formed so as to be spaced apartfrom each other on the insulating film 4 a. Thus, the p-side padelectrodes 12 and 13 are electrically isolated from each other.

As shown in FIG. 3 (b), an insulating film 4 b having a predeterminedwidth is formed on the insulating film 4 a and the p-side pad electrode12. The insulating film 4 b is formed such that one end of the p-sidepad electrode 12 extending in the Y-direction is exposed. A wire fordriving the blue-violet semiconductor laser device 1 is bonded to theexposed one end of the p-side pad electrode 12. A region having a widthof approximately 100 μm and having a length of approximately 100 μm atthe one end of the p-side pad electrode 12 extending in the Y-directionis exposed.

As shown in FIG. 4 (c), a p-side pad electrode 14 is formed on theinsulating film 4 a and the insulating film 4 b. The p-side padelectrode 14 extends in the X-direction on the insulating film 4 a andthe insulating film 4 b, and its part extends in the Y-direction,similarly to the p-side pad electrode 13, at a position spaced apartfrom the p-side pad electrode 13. Consequently, the p-side padelectrodes 12, 13, and 14 are electrically isolated from one another.

As shown in FIG. 4 (d), an insulating film 4 c is formed in apredetermined pattern on the insulating film 4 a and the p-side padelectrodes 13 and 14. The insulating film 4 c is formed such thatrespective one ends of the p-side pad electrodes 13 and 14 extending inthe Y-direction are exposed. Wires for driving the red semiconductorlaser device 2 and the infrared semiconductor laser device 3 arerespectively bonded to the exposed one ends of the p-side pad electrodes13 and 14.

Regions each having a width of approximately 100 μm and having a lengthof approximately 100 μm at the respective one ends of the p-side padelectrodes 13 and 14 extending in the Y-direction are exposed.

Furthermore, the insulating film 4 c is formed such that a substantiallycentral portion of the p-side pad electrode 13 is exposed. A solder filmH composed of Au—Sn is formed in the exposed portion of the p-side padelectrode 13. A solder film H composed of Au—Sn is also formed in apredetermined region on the p-side pad electrode 14.

The monolithic red/infrared semiconductor laser device 23X is joined tothe blue-violet semiconductor laser device 1 shown in FIG. 2 such thatthe p-side pad electrode 22 in the red semiconductor laser device 2 isjoined to the p-side pad electrode 13 with the solder film H sandwichedtherebetween and the p-side pad electrode 32 in the infraredsemiconductor laser device 3 is joined to the p-side pad electrode 14with the solder film H sandwiched therebetween.

Thus, the p-side pad electrode 22 in the red semiconductor laser device2 is electrically connected to the p-side pad electrode 13, and thep-side pad electrode 32 in the infrared semiconductor laser device 3 iselectrically connected to the p-side pad electrode 14.

Since the monolithic red/infrared semiconductor laser device 23X isjoined to the patterned insulating film 4 c in the foregoing, the p-sidepad electrode 32 in the infrared semiconductor laser device 3 isprevented from coming into contact with the p-side pad electrode 14.

A voltage is applied between the p-side pad electrode 12 and then-electrode 15 in the blue-violet semiconductor laser device 1 so that alaser beam having a wavelength of approximately 405 nm is emitted in theX-direction from a region (hereinafter referred to as a blue-violetemission point) 11 below the projection T1 on the p-n junction interface10.

A voltage is applied between the p-side pad electrode 22 in the redsemiconductor laser device 2 (the p-side pad electrode 13 on theblue-violet semiconductor laser device 1) and the common n-electrode 233so that a laser beam having a wavelength of approximately 650 nm isemitted in the X-direction from a predetermined region (hereinafterreferred to as a red emission point) 21 on the p-n junction interface20.

A voltage is applied between the p-side pad electrode 32 in the infraredsemiconductor laser device 3 (the p-side pad electrode 14 on theblue-violet semiconductor laser device 1) and the common n-electrode 233so that a laser beam having a wavelength of approximately 780 nm isemitted in the X-direction from a predetermined region (hereinafterreferred to as an infrared emission point) 31 on the p-n junctioninterface 30.

In the present embodiment, the monolithic red/infrared semiconductorlaser device 23X is arranged such that the projection T1 in theblue-violet semiconductor laser device 1 and the projection T3 in theinfrared semiconductor laser device 3 are opposed to each other. Thus,the distance between the blue-violet emission point 11 and the infraredemission point 31 is shorter than both the distance between theblue-violet emission point 11 and the red emission point 31 and thedistance between the red emission point 21 and the infrared emissionpoint 31.

In the present embodiment, the distance between the red emission point21 and the infrared emission point 31 in the Y-direction is adjusted toapproximately 100 μm, for example.

The width of the blue-violet semiconductor laser device 1 in theY-direction is approximately 400 μm, for example. The width of themonolithic red/infrared semiconductor laser device 23X in theY-direction is approximately 200 μm, for example.

It is preferable that the distance between the blue-violet emissionpoint 11 and the infrared emission point 31 is not more than 20 μm.

The cross-sectional view of FIG. 2 is enlarged in the Z-direction.Actually, the distance between the emission points in the Z-direction issignificantly shorter than the distance between the emission points inthe Y-direction. In the actual semiconductor laser apparatus 1000A,therefore, the blue-violet emission point 11 and the red emission point21 are positioned on a substantially straight line along an axisparallel to the Y-direction.

(b) Effect of Semiconductor Laser Apparatus

As shown in FIG. 1, in the semiconductor laser apparatus 1000A accordingto the present embodiment, respective one ends of the p-side padelectrodes 12, 13, and 14 extending in the Y-direction are exposed,projecting from a side surface of the monolithic red/infraredsemiconductor laser device 23X in the Y-direction through an areabetween the blue-violet semiconductor laser device 1 and the monolithicred/infrared semiconductor laser device 23X on the insulating film 4 ain the blue-violet semiconductor laser device 1. Thus, the respectiveexposed portions of the p-side pad electrodes 13 and 14 extending in theY-direction are arranged on a substantially straight line in theX-direction, so that the width in the Y-direction of the blue-violetsemiconductor laser device 1 can be reduced.

The exposed portions of the p-side pad electrodes 13 and 14 extending inthe Y-direction are arranged on the substantially straight line in theX-direction, so that an arrangement space of the red semiconductor laserdevice 2 and the infrared semiconductor laser device 3 on theblue-violet semiconductor laser device 1 in the Y-direction can beincreased. Consequently, the respective widths of the red semiconductorlaser device 2 and the infrared semiconductor laser device 3 in theY-direction can be increased.

The p-side pad electrodes 12 and 13 can be simultaneously formed, sothat the manufacturing processes can be simplified.

As described above, the length in the Z-direction of the redsemiconductor laser device 2 is larger than the length in theZ-direction of the infrared semiconductor laser device 3. The surface ofthe semiconductor layer on the side of the lower surface of theprojection T2 in the red semiconductor laser device 2 projects towardthe blue-violet semiconductor laser device 1 in the Z-direction fartherthan the surface of the semiconductor layer on the side of the lowersurface of the projection T3 in the infrared semiconductor laser device3. When the monolithic red/infrared semiconductor laser device 23X isjoined to the blue-violet semiconductor laser device 1, therefore, alarge stress can be prevented from being created on the junction planeof the infrared semiconductor laser device 3 and the blue-violetsemiconductor laser device 1. As a result, respective damages to theprojections T1 and T3 can be reduced. Further, the monolithicred/infrared semiconductor laser device 23X can be stacked substantiallyparallel to the blue-violet semiconductor laser device 1. Thus, themonolithic red/infrared semiconductor laser device 23X can be reliablyjoined to the blue-violet semiconductor laser device 1.

The monolithic red/infrared semiconductor element 23X can be stackedsubstantially parallel to the blue-violet semiconductor laser device 1by making the length in the Z-direction of the red semiconductor laserdevice 2 larger than the length in the Z-direction of the infraredsemiconductor laser device 3. Thus, the monolithic red/infraredsemiconductor laser device 23X can be joined to the blue-violetsemiconductor laser device 1 in a stable state.

(c) State where Semiconductor Laser Apparatus is Mounted on Package forLaser Devices

The semiconductor laser apparatus 1000A shown in FIGS. 1 and 2 ismounted within a package for laser devices. FIG. 5 is a perspective viewshowing the appearance of a substantially round-shaped can package forlaser devices 500 on which the semiconductor laser apparatus 1000A shownin FIG. 1 is mounted.

In FIG. 5, the substantially round-shaped can package for laser devices500 comprises a package main body 503 having electrically conductiveproperties, power feed pins 501 a, 501 b, 501 c, and 502, and a cover504.

The package main body 503 is provided with the semiconductor laserapparatus 1000A shown in FIGS. 1 and 2, and is sealed with the cover504. The cover 504 is provided with an extraction window 504 a. Theextraction window 504 a is composed of a material transmitting a laserbeam. The power feed pin 502 is mechanically and electrically connectedto the package main body 503. The power feed pin 502 is used as a groundterminal.

Respective one ends of the power feed pins 501 a, 501 b, 501 c, and 502extending outward from the package main body 503 are connected todriving circuits (not shown).

Wiring using wires of the semiconductor laser apparatus 1000A mountedwithin the substantially round-shaped can package for laser devices 500will be described. Description is made, taking the side on which a laserbeam from a semiconductor laser device is emitted as a front.

FIG. 6 is a schematic front view showing a state where the cover 504 inthe substantially round-shaped can package for laser devices 500 shownin FIG. 5 is removed, and FIG. 7 is a schematic top view showing a statewhere the cover 504 in the substantially round-shaped can package forlaser devices 500 shown in FIG. 5 is removed. In FIG. 6, thesemiconductor laser apparatus 1000A provided in the substantiallyround-shaped can package for laser devices 500 is indicated by a crosssection taken along a line A1-A1 shown in FIG. 1. In FIGS. 6 and 7, anX-direction, a Y-direction, and a Z-direction are also defined, as inFIG. 1.

As shown in FIG. 6, a submount 505S having electrically conductiveproperties is provided on a supporting member 505 having electricallyconductive properties that is integrated with the package main body 503.The supporting member 505 and the submount 505S are composed of amaterial superior in electrically conductive properties and thermallyconductive properties.

The semiconductor laser apparatus 1000A is joined to the submount 505Swith an adhesion layer (solder) 505H sandwiched therebetween. Thesemiconductor laser apparatus 1000A adheres to the submount 505S (theadhesion layer 505H) such that the blue-violet emission point 11 in theblue-violet semiconductor laser device 1 is positioned in asubstantially central portion of the substantially round-shaped canpackage for laser devices 500 on a Y-Z plane, i.e., at the center of theextraction window 504 a in the cover 504 (see FIG. 5).

As shown in FIGS. 6 and 7, the power feed pins 501 a, 501 b, and 501 care electrically insulated from the package main body 503, respectively,by insulating rings 501 z.

The power feed pin 501 a is connected to one end of the p-side padelectrode 14 in the semiconductor laser apparatus 1000A through a wireW1. The power feed pin 501 b is connected to one end of the p-side padelectrode 12 in the semiconductor laser apparatus 1000A through a wireW2. The power feed pin 501 c is connected to one end of the p-side padelectrode 13 in the semiconductor laser apparatus 1000A through a wireW3.

On the other hand, the exposed upper surface of the supporting member505 and the common n-electrode 233 in the semiconductor laser apparatus1000A are electrically connected to each other through a wire W4.

Here, the supporting member 505 is electrically connected through thesubmount 505S and the adhesion layer 505H. Thus, the power feed pin 502is electrically connected to the n-electrode 15 in the blue-violetsemiconductor laser device 1 and the n-electrode 233 that is commonbetween the red semiconductor laser device 2 and the infraredsemiconductor laser device 3. That is, common cathode wire connection ofthe blue-violet semiconductor laser device 1, the red semiconductorlaser device 2, and the infrared semiconductor laser device 3 isimplemented.

The blue-violet semiconductor laser device 1 can be driven by applying avoltage between the power feed pin 501 b and the power feed pin 502. Theinfrared semiconductor laser device 3 can be driven by applying avoltage between the power feed pin 501 a and the power feed pin 502. Thered semiconductor laser device 2 can be driven by applying a voltagebetween the power feed pin 501 c and the power feed pin 502. Thus, theblue-violet semiconductor laser device 1, the red semiconductor laserdevice 2, and the infrared semiconductor laser device 3 can beindependently driven.

In the semiconductor laser apparatus 1000A according to the presentembodiment, the p-side pad electrodes 12, 13, and 14 are electricallyisolated from one another, as described above. Thus, arbitrary voltagescan be respectively applied to the p-side pad electrodes 12, 13, and 14in the blue-violet semiconductor laser device 1, the red semiconductorlaser device 2, and the infrared semiconductor laser device 3.Consequently, a system for driving the blue-violet semiconductor laserdevice 1, the red semiconductor laser device 2, and the infraredsemiconductor laser device 3 can be arbitrary selected.

(d) Effect in State Where Semiconductor Laser Apparatus is Mounted onPackage for Laser Devices

As described in the foregoing, the distance between the blue-violetemission point 11 and the infrared emission point 21 is shorter thanboth the distance between the blue-violet emission point 11 and the redemission point 31 and the distance between the red emission point 21 andthe infrared emission point 31. That is, the laser beam from theblue-violet semiconductor laser device 1 and the laser beam from theinfrared semiconductor laser device 3 are respectively emitted frompositions in close proximity to each other.

The wavelength (approximately 780 nm) of the laser beam from theinfrared semiconductor laser device 3 is substantially equal to anatural number times (approximately two times) the wavelength(approximately 405 nm) of the laser beam from the blue-violetsemiconductor laser device 1. In this case, a diffraction efficiency ina case where the laser beam from the blue-violet semiconductor laserdevice 1 is incident on the diffraction grating and a diffractionefficiency in a case where the laser beam from the infraredsemiconductor laser device 3 is incident on the diffraction grating cansubstantially be equalized. Then, because the wavelength (approximately650 nm) of the laser beam from the red semiconductor laser device 2differs from a natural number times the wavelength of the laser beamfrom the blue-violet semiconductor laser device 1, a diffractionefficiency in a case where the laser beam from the blue-violetsemiconductor laser device 1 is incident on the diffraction grating anda diffraction efficiency in a case where the laser beam from the redsemiconductor laser device 2 is incident on the diffraction gratingdiffer from each other. Therefore, when a first-order diffraction lightbeam of the red semiconductor laser beam is enhanced, zeroth-orderdiffracted light beams of the blue-violet semiconductor laser beam andthe infrared semiconductor laser beam can simultaneously be enhanced byadjustment of height of the diffraction grating.

Then, in a case where the laser beam from the blue-violet semiconductorlaser device 1, the laser beam from the infrared semiconductor laserdevice 3, and the laser beam from the red semiconductor element 2 areincident on the diffraction grating, therefore, the zeroth-orderdiffracted laser beam from the blue-violet semiconductor laser device 1and the zeroth-order diffracted laser beam from the infraredsemiconductor laser device 3 are diffracted at the same angle by thediffraction grating. As described above, the distance between theblue-violet semiconductor laser device 1 and the infrared semiconductorelement 3 is very short, so that the respective optical axes of thelaser beams from the blue-violet semiconductor laser device 1 and theinfrared semiconductor element 3 that have been diffracted by thediffraction grating almost coincide with each other.

On the other hand, the first-order diffracted laser beam from the redsemiconductor laser device 2 and the zeroth-order diffracted laser beamfrom the blue-violet semiconductor laser device 1 are diffracted atdifferent angles from each other by the diffraction grating, and thefirst-order diffracted laser beam from the red semiconductor laserdevice 2 and the zeroth-order diffracted laser beam from the infraredsemiconductor laser device 3 are diffracted at different angles fromeach other by the diffraction grating. Consequently, the position of afocusing spot of the laser beam from the red semiconductor laser device2 can be matched with the position of focusing spots of the laser beamsfrom the blue-violet semiconductor laser device 1 and the infraredsemiconductor laser device 3 on a photodetector utilizing such adifference in diffraction efficiency.

As a result, the respective laser beams from the blue-violetsemiconductor laser device 1, the red semiconductor laser device 2, andthe infrared semiconductor laser device 3 can be received by onephotodetector. The details will be described later.

The intensity of the laser beam from the blue-violet semiconductor laserdevice 1 is weaker than the respective intensities of the laser beamsfrom the red semiconductor laser device 2 and the infrared semiconductorlaser device 3. In this example, the blue-violet emission point 11 inthe blue-violet semiconductor laser device 1 is positioned at the centerof the extraction window 504 a in the cover 504. Thus, the laser beamfrom the blue-violet semiconductor laser device 1 is emitted from thecenter of the substantially round-shaped can package for laser devices500.

Even if the substantially round-shaped can package for laser devices 500is rotated around the central axis of the substantially round-shaped canpackage for laser devices 500, therefore, the change in the position ofthe axis of the laser beam emitted from the blue-violet semiconductorlaser device 1 can be reduced. Consequently, the angle of an opticalsystem such as a lens and the angle of the substantially round-shapedcan package for laser devices 500 can be easily adjusted with respect tothe central axis of the substantially round-shaped can package for laserdevices 500 while increasing the light extraction efficiency of theblue-violet semiconductor laser device 1. As a result, the opticalsystem is easy to design.

As shown in FIGS. 6 and 7, the exposed portion of the p-side padelectrode 13 in the red semiconductor laser device 2 is provided so asto be positioned farther apart from a laser beam emission facet than theexposed portion of the p-side pad electrode 14 in the infraredsemiconductor laser device 3. Therefore, the p-side pad electrode 13 canbe easily connected to the power feed pin 501 c opposed to a surface, onwhich the semiconductor laser apparatus is mounted, of the supportingmember 505, and the length of the wire W3 can be shortened.

In this example, as shown in FIG. 7, the power feed pin 501 a projectstoward the laser beam emission facet farther than the power feed pin 501c. In this case, it is possible to easily connect the exposed portion ofthe p-side pad electrode 14 provided at a position closer to the laserbeam emission facet than the exposed portion of the p-side pad electrode13 to the power feed pin 501 a. Further, the length of the wire W1 canbe shortened.

Although in this example, the exposed portion of the p-side padelectrode 14 in the infrared semiconductor laser device 3 is arranged onthe side of the laser beam emission facet of the semiconductor laserapparatus 1000A in the X-direction, the exposed portion of the p-sidepad electrode 13 in the red semiconductor laser device 2 may be arrangedon the side of the laser beam emission facet of the semiconductor laserapparatus 1000A in the X-direction. In this case, the p-side padelectrode 14 in the infrared semiconductor laser device 3 and the powerfeed pin 501 c are connected to each other through a wire. Further, thep-side pad electrode 13 in the red semiconductor laser device 2 and thepower feed pin 501 a are connected to each other through a wire.

(e) Method of Manufacturing Semiconductor Laser Apparatus

A method of manufacturing the semiconductor laser apparatus 1000Aaccording to the present embodiment will be described. FIGS. 8 to 11 areschematic sectional views showing an example of a method ofmanufacturing the semiconductor laser apparatus 1000A according to thefirst embodiment. In FIGS. 8 to 11, an X-direction, a Y-direction, and aZ-direction shown in FIG. 1 are also defined.

Respective cross sections shown in FIGS. 8 to 11 correspond to a crosssection taken along the line A1-A1 shown in FIG. 1. An n-GaN substrate 1s and an n-GaAs substrate 50, described later, are respectively an n-GaNwafer and an n-GaAs wafer. A plurality of blue-violet semiconductorlaser devices 1 and monolithic red/infrared semiconductor laser devices23X are respectively formed in the n-GaN wafer and the n-GaAs wafer.Consequently, respective parts of the n-GaN wafer and the n-GaAs waferare illustrated in FIGS. 8 to 11.

As shown in FIG. 8 (a), in order to manufacture the blue-violetsemiconductor laser device 1, a semiconductor layer lt having amultilayer structure is formed on one surface of the n-GaN substrate isserving as a first growth substrate, to form a projection T1, extendingin the X-direction is formed in the semiconductor layer lt. Thereafter,an insulating film 4 a composed of SiO₂ is formed on an upper surface ofthe semiconductor layer lt having the projection T1 formed therein.Further, the insulating film 4 a on an upper surface of the projectionT1 is removed, to form a p-type ohmic electrode 621 on the exposedprojection T1.

As shown in FIG. 8 (b), p-side pad electrodes 12 and 13 are then formedby patterning on an upper surface of the p-type ohmic electrode 621 andon the insulating film 4 a on both sides of the projection T1 (see FIG.3 (a)).

As shown in FIG. 8 (c), an insulating film 4 b is then formed in apredetermined region on the insulating film 4 a and on the p-side padelectrode 12 (see FIG. 3 (b)).

As shown in FIG. 9 (d), a p-side pad electrode 14 is formed bypatterning in a predetermined region on the insulating film 4 a and theinsulating film 4 b (see FIG. 4 (c)).

As shown in FIG. 9 (e), an insulating film 4 c is then formed bypatterning in a predetermined region on each of the insulating film 4 aand the p-side pad electrodes 13 and 14 (see FIG. 4 (d)). Therefore, asolder film H composed of Au—Sn is formed on each of an upper surface ofthe exposed p-side pad electrode 13 and in a predetermined region of theexposed p-side pad electrode 14. An n-electrode 15 in the blue-violetsemiconductor laser device 1 is formed in the subsequent steps.

On the other hand, as shown in FIG. 10 (f), in order to manufacture themonolithic/infrared semiconductor laser device 23X, an etching stoplayer 51 composed of AlGaAs is formed on one surface of an n-GaAssubstrate 50 serving as a second growth substrate, to form an n-GaAscontact layer 5 on the etching stop layer 51.

A semiconductor layer 2 t having an AlGaInP based multilayer structureand a semiconductor layer 3 t having an AlGaAs based multilayerstructure are formed so as to be spaced apart from each other on then-GaAs contact layer 5. Further, a p-side pad electrode 22 and a p-sidepad electrode 32 are respectively formed on the semiconductor layer 2 tand the semiconductor layer 3 t. P-type ohmic electrodes arerespectively formed between the semiconductor layer 2 t and the p-sidepad electrode 22 and between the semiconductor layer 3 t and the p-sidepad electrode 32, which are omitted in the figure. The commonn-electrode 233 in the monolithic red/infrared semiconductor laserdevice 23X is formed in the subsequent steps.

As shown in FIG. 10 (g), the p-side pad electrode 13 formed on theinsulating film 4 a and the p-side pad electrode 22 formed on thesemiconductor layer 2 t are joined to each other with the solder film Hsandwiched therebetween, and the p-side pad electrode 14 formed on theinsulating film 4 a and the insulating film 4 b and the p-side padelectrode 32 formed on the semiconductor layer 3 t are joined to eachother with the solder film H sandwiched therebetween, thereby forming astacked substrate.

At this time, both the n-GaN substrate 1 s and the n-GaAs substrate 50respectively have thicknesses of approximately 300 to 500 μm. Thus, then-GaN substrate 1 s and the n-GaAs substrate 50 are easy to handle, sothat the p-side pad electrodes 22 and 32 are respectively easy to jointo the p-side pad electrodes 13 and 14.

The n-GaN substrate is in the blue-violet semiconductor laser device 1is transparent. The n-GaN substrate is has such a transmission factorand a thickness that the monolithic red/infrared semiconductor laserdevice 23X can be visually observed through the n-GaN substrate 1 s.

Thus, positions where the p-side pad electrodes 22 and 32 arerespectively joined to the p-side pad electrodes 13 and 14 can bevisually confirmed through the n-GaN substrate 1 s. Thus, themonolithic/infrared semiconductor laser device 23X (the redsemiconductor laser device 2 and the infrared semiconductor laser device3) on the blue-violet semiconductor laser device 1 is easy to position.

In the present embodiment, a substrate in the blue-violet semiconductorlaser device 1 is not limited to the n-GaN substrate is. For example,another substrate having translucent properties and electricallyconductive properties may be used. As the other substrate havingtranslucent properties, an n-ZnO substrate can be used, for example. Inthis case, the monolithic red/infrared semiconductor laser device 23X iseasy to position on the blue-violet semiconductor laser device 1, asdescribed above.

Here, the n-GaAs substrate 50 is processed to a predetermined thicknessby etching, grinding, or the like, and is then etched up to the etchingstop layer 51.

For example, the n-GaAs substrate 50 is first ground until it has apredetermined thickness, and is then removed by dry etching such asreactive ion etching (RIE).

The etching stop layer 51 is further removed. For example, the etchingstop layer 51 is removed by wet etching using an etchant composed of ahydrofluoric acid or a hydrochloric acid.

Thereafter, as shown in FIG. 11 (h), the etching stop layer 51 isremoved, and the common n-electrode 233 is then formed by patterning inrespective regions on the n-GaAs contact layer 5 above the semiconductorlayers 2 t and 3 t and a predetermined region therebetween.

As shown in FIG. 11 (i), the n-GaAs contact layer 5 in a portion wherethe common n-electrode 233 is not formed is removed by dry etching.Thus, the monolithic red/infrared semiconductor laser device 23X (thered semiconductor laser device 2 and the infrared semiconductor laserdevice 3) is manufactured. The details of the configuration of the redsemiconductor laser device 2 and the infrared semiconductor laser device3 will be described later.

Furthermore, the n-GaN substrate 1 s is thinned by grinding, and then-electrode 15 is then formed on a lower surface of the n-GaN substrateis. Thus, the blue-violet semiconductor laser device 1 is manufactured.The details of the configuration of the blue-violet semiconductor laserdevice 1 will be described later.

Finally, a stacked substrate composed of the blue-violet semiconductorlaser device 1 and the monolithic red/infrared semiconductor laserdevice 23X that are formed as described above is cleaved along aplurality of lines parallel to the Y-direction, to form cavity facets.Here, the cleavage along the Y-direction is performed such that therespective cavity lengths (in the X-direction) of the blue-violetsemiconductor laser device 1 and the monolithic red/infraredsemiconductor laser device 23X will be approximately 700 μm, forexample.

A protective film is formed on each of the cavity facets and is then cutalong a plurality of lines parallel to the X-direction, to divide thesemiconductor laser apparatus 1000A into a plurality of chips. Thecutting of the stacked substrate along the X-direction is performedalong a one-dot and dash line CT1 shown in FIG. 11 (g), for example.

Chips of the blue-violet semiconductor laser device 1 and chips of themonolithic red/infrared semiconductor laser device 23X may be previouslyindividually formed, and may be affixed to one another to manufacturethe semiconductor laser apparatus 100A.

(f) Configuration of Blue-Violet Semiconductor Laser Device

The details of the configuration of the blue-violet semiconductor laserdevice 1, together with a method of manufacturing the same, will bedescribed on the basis of FIG. 12.

FIG. 12 is a schematic sectional view for explaining the details of theconfiguration of the blue-violet semiconductor laser device 1. In thefollowing description, an X-direction, a Y-direction, and a Z-directionare also defined, as in FIG. 1.

When the blue-violet semiconductor laser device 1 is manufactured, thesemiconductor layer lt having a multilayer structure is formed on then-GaN substrate is, as described above.

As shown in FIG. 12 (a), an n-GaN layer 101, an n-AlGaN cladding layer102, an n-GaN optical guide layer 103, a multiple quantum well (MQW)active layer 104, an undoped AlGaN cap layer 105, an undoped GaN opticalguide layer 106, a p-AlGaN cladding layer 107, and an undoped GaInNcontact layer 108 are formed in this order as the semiconductor layer ithaving a multilayer structure on the n-GaN substrate is. The layers areformed by metal organic chemical vapor deposition (MOCVD), for example.

As shown in FIG. 12 (b), the MQW active layer 104 has a structure inwhich four undoped GaInN barrier layers 104 a and three undoped GaInNwell layer 104 b are alternately stacked.

Here, the Al composition of the n-AlGaN cladding layer 102 is 0.15, andthe Ga composition thereof is 0.85. Si is doped into the n-GaN layer101, the n-AlGaN cladding layer 102, and the n-GaN optical guide layer103.

The Ga composition of the undoped GaInN barrier layer 104 a is 0.95, andthe In composition thereof is 0.05. The Ga composition of the undopedGaInN well layer 104 b is 0.90, and the In composition thereof is 0.10.The Al composition of the p-AlGaN cap layer 105 is 0.30, and the Gacomposition thereof is 0.70.

Furthermore, the Al composition of the p-AlGaN cladding layer 107 is0.15, and the Ga composition thereof is 0.85. Mg is doped into thep-AlGaN cladding layer 107. The Ga composition of the undoped GaInNcontact layer 108 is 0.95, and the In composition thereof is 0.05.

A striped ridge Ri1 extending in the X-direction is formed in thep-AlGaN cladding layer 107 in the semiconductor layer 1 t.

The undoped GaInN contact layer 108 is formed on an upper surface of theridge Ri in the p-AlGaN cladding layer 107. Thus, a projection T1comprising the ridge Ri1 in the p-AlGaN cladding layer 107 and theundoped GaInN contact layer 108 is formed. The width L1 at the top ofthe projection T1 is approximately 1.5 μm, and the height H1 of theridge Ri1 is approximately 0.3 μm.

An insulating film 4 a composed of SiO₂ is formed on respective uppersurfaces of the p-AlGaN cladding layer 107 and the undoped GaInN contactlayer 108. The insulating film 4 a formed on the undoped GaInN contactlayer 108 is removed by etching. A p-type ohmic electrode 621 composedof Pd/Pt/Au is formed on the undoped GaInN contact layer 108 exposed tothe exterior. Further, a p-side pad electrode 12 is formed bysputtering, vacuum evaporation, or electron beam evaporation so as tocover respective upper surfaces of the p-type ohmic electrode 621 andthe insulating film 4 a. Here, the description of the p-side padelectrodes 13 and 14 shown in FIG. 1 is not repeated.

The semiconductor layer it having a multilayer structure is thus formedon one surface of the n-GaN substrate 1 s. Further, an n-electrode 15composed of Ti/Pt/Au is formed on the other surface of the n-GaNsubstrate 1 s.

In the blue-violet semiconductor laser device 1, a blue-violet emissionpoint 11 is formed at a position of the MQW active layer 104 below theridge Ri1. In this example, the MQW active layer 104 corresponds to thep-n junction interface 10 shown in FIG. 1.

(g) Configuration of Red Semiconductor Laser Device

The details of the configuration of the red semiconductor laser device2, together with a method of manufacturing the same, will be describedon the basis of FIG. 13.

FIG. 13 is a schematic sectional view for explaining the details of theconfiguration of the red semiconductor laser device 2 in the monolithicred/infrared semiconductor laser device 23X. In the followingdescription, an X-direction, a Y-direction, and a Z-direction are alsodefined, as in FIG. 1. Although in the present embodiment, the redsemiconductor laser device 2 is manufactured by forming thesemiconductor layer 2 t on an n-GaAs contact layer 5, the semiconductorlayer 2 t is formed on an n-GaAs substrate 5X in place of the n-GaAscontact layer 5. Si is doped into the n-GaAs substrate 5X.

As shown in FIG. 13 (a), an n-GaN layer 201, an n-AlGInP cladding layer202, an undoped AlGaInP optical guide layer 203, an MQW active layer204, an undoped AlGaInP optical guide layer 205, a p-AlGaInP claddinglayer 206, and a p-contact layer 207 are formed in this order on then-GaAs substrate 5X. The layers are formed by MOCVD, for example.

As shown in FIG. 13 (b), the MQW active layer 204 has a structure inwhich two undoped AlGaInP barrier layers 204 a and three undoped InGaPwell layers 204 b are alternately stacked.

Here, the Al composition of the n-AlGaInP cladding layer 202 is 0.35,the Ga composition thereof is 0.15, and the In composition thereof is0.50. Si is doped into the n-GaAs layer 201 and the n-AlGaInP claddinglayer 202.

The Al composition of the undoped AlGaInP optical guide layer 203 is0.25, the Ga composition thereof is 0.25, and the In composition thereofis 0.50.

The Al composition of the undoped AlGaInP barrier layer 204 a is 0.25,the Ga composition thereof is 0.25, and the In composition thereof is0.50. The In composition of the undoped InGaP well layer 204 b is 0.50,and the Ga composition thereof is 0.50. The Al composition of theundoped AlGaInP optical guide layer 205 is 0.25, the Ga compositionthereof is 0.25, and the In composition thereof is 0.50.

Furthermore, the Al composition of the p-AlGaInP cladding layer 206 is0.35, the Ga composition thereof is 0.15, and the In composition thereofis 0.50. The In composition of the p-InGaP etching stop layer 207 is0.50, and the Ga composition thereof is 0.50.

The p-contact layer 207 has a multilayer structure of a p-GaInP layerand a p-GaAs layer. The Ga composition of the p-GaInP is 0.5, and the Incomposition thereof is 0.5.

When the composition of the AlGaInP based material is expressed by ageneral formula AlaGabIncP, a indicates the Al composition, b indicatesthe Ga composition, and c indicates the In composition.

Zn is doped into p-GaInP and p-GaAs in the p-AlGaInP cladding layer 206and the p-contact layer 207.

In the foregoing, a striped ridge Ri2 extending in the X-direction isformed in the p-AlGaN cladding layer 206. The p-contact layer 207 isformed on an upper surface of the ridge Ri2 in the p-AlGaInP claddinglayer 206.

A current blocking layer 208 is formed so as to cover an upper surfaceof the p-AlGaInP cladding layer 206, a side surface of the ridge Ri2,and a side surface of the p-contact layer 207. The current blockinglayer 208 is composed of AlGaAs having Si doped therein.

A contact layer 209 is formed on the p-contact layer 207 and the currentblocking layer 208. Thus, a projection T2 comprising the ridge Ri2 inthe p-AlGaInP cladding layer 206, the p-contact layer 207, the currentblocking layer 208, and the contact layer 209 is formed. The contactlayer 209 is composed of GaAs having Zn doped therein. The width L2 atthe top of the projection T2 is approximately 10 μm, and the height H2of the ridge Ri2 is approximately 1 μm.

A p-side pad electrode 22 is formed by sputtering, vacuum evaporation,or electron beam evaporation on the contact layer 209.

The semiconductor layer 2 t having a multilayer structure is thus formedon one surface of the n-GaAs substrate 5X. Further, an n-electrode 23 (acommon n-electrode 233) composed of AuGe/Ni/Au is formed on the othersurface of the n-GaAs substrate 5X.

In the red semiconductor laser device 2, a red emission point 21 isformed at a position of the MQW active layer 204 below the ridge Ri2. Inthis example, the MQW active layer 204 corresponds to the p-n junctioninterface 20 shown in FIG. 1.

(h) Configuration of Infrared Semiconductor Laser Device

The details of the configuration of the infrared semiconductor laserdevice 3, together with a method of manufacturing the same, will bedescribed on the basis of FIG. 14.

FIG. 14 is a schematic sectional view for explaining the details of theconfiguration of the infrared semiconductor laser device 3 in themonolithic red/infrared semiconductor laser device 23X. In the followingdescription, an X-direction, a Y-direction, and a Z-direction are alsodefined, as in FIG. 1. Although in the present embodiment, the infraredsemiconductor laser device 3 is manufactured by forming thesemiconductor layer 3 t on the n-GaAs contact layer 5, the semiconductorlayer 3 t is formed on an n-GaAs substrate 5X in place of the n-GaAscontact layer 5. Si is doped into the n-GaAs substrate 5X.

As shown in FIG. 14 (a), an n-GaN layer 301, an n-AlGaAs cladding layer302, an undoped AlGaAs optical guide layer 303, an MQW active layer 304,an undoped AlGaAs optical guide layer 305, a p-AlGaAs cladding layer306, and a p-contact layer 307 are formed in this order as thesemiconductor layer 3 t having a multilayer structure on the n-GaAssubstrate 5X. The layers are formed by MOCVD, for example.

As shown in FIG. 14 (b), the MQW active layer 304 has a structure inwhich two undoped AlGaAs barrier layers 304 a and three undoped AlGaAswell layers 304 b are alternately stacked.

Here, the Al composition of the n-AlGaAs cladding layer 302 is 0.45, andthe Ga composition thereof is 0.55, for example. Si is doped into then-GaAs layer 301 and the n-AlGaAs cladding layer 302.

The Al composition of the undoped AlGaAs optical guide layer 303 is0.35, and the Ga composition thereof is 0.65. The Al composition of theundoped AlGaAs barrier layer 304 a is 0.35, and the Ga compositionthereof is 0.65. The Al composition of the undoped AlGaAs well layer 304b is 0.10, and the Ga composition thereof is 0.90. The Al composition ofthe undoped AlGaAs optical guide layer 305 is 0.35, and the Gacomposition thereof is 0.65.

Furthermore, the Al composition of the p-AlGaN cladding layer 306 is0.45, and the Ga composition thereof is 0.55.

Zn is doped into the p-AlGaAs cladding layer 306 and the p-contact layer307.

In the foregoing, a striped ridge Ri3 extending in the X-direction isformed in the p-AlGaAs cladding layer 306. The p-contact layer 307 isformed on an upper surface of the ridge Ri3 in the p-AlGaAs claddinglayer 306.

A current blocking layer 308 is formed so as to cover an upper surfaceof the p-AlGaAs cladding layer 306, a side surface of the ridge Ri3, anda side surface of the p-contact layer 307. The current blocking layer308 is composed of AlGaAs having Si doped therein.

A cap layer 309 is formed so as to cover the top of the current blockinglayer 308 and the exposed side surface of the p-contact layer 307. Thus,a projection T3 comprising the ridge Ri3 in the p-AlGaAs cladding layer306, the p-contact layer 307, the current blocking layer 308, and thecap layer 309 is formed. The cap layer 309 is composed of undoped GaAs.The width L3 of the projection T3 is approximately 15 μm, and the heightH3 of the ridge Ri3 is approximately 1 μm.

A p-side pad electrode 32 is formed by sputtering, vacuum evaporation,or electron beam evaporation on the p-contact layer 307 and in apredetermined region on the cap layer 309.

The semiconductor layer 3 t having a multilayer structure is thus formedon one surface of the n-GaAs substrate 5X. Further, an n-electrode 33 (acommon n-electrode 233) composed of AuGe/Ni/Au is formed on the othersurface of the n-GaAs substrate 5X.

In the infrared semiconductor laser device 3, an infrared emission point31 is formed at a position of the MQW active layer 304 below the ridgeRi3. In this example, the MQW active layer 304 corresponds to the p-njunction interface 30 shown in FIG. 1.

Here, in the present embodiment, the width in the Y-direction at the topof the projection T3 is larger than the width in the Y-direction at thetop of the projection T1 (see FIG. 12), as described above. In thiscase, the projection T3 can be stably arranged on the projection T1 injoining the blue-violet semiconductor laser device 1 and the infraredsemiconductor laser device 3. The projection T3 is prevented fromapplying a local stress to the projection T1. Thus, the blue-violetsemiconductor laser device 1 is prevented from being degraded.

In the present embodiment, the width in the Y-direction at the top ofthe projection T3 is larger than the width in the Y-direction at the topof the projection T2, as described above. In this case, the projectionT3 can be more stably arranged on the projection T1. The projection T3is reliably prevented from applying a local stress to the projection T1.Consequently, the blue-violet semiconductor laser device 1 is reliablyprevented from being degraded.

(i) Configuration of Optical Pickup Apparatus Containing SemiconductorLaser Apparatus

A plurality of examples of an optical pickup apparatus containing thesemiconductor laser apparatus according to the present embodiment willbe described.

(i-1a) First Example of Optical Pickup Apparatus

FIG. 15 is a diagram showing the configuration of an optical pickupapparatus 900 a according to the present embodiment. In the followingdescription, a laser beam having a wavelength of approximately 405 nmemitted from the blue-violet emission point 11 in the semiconductorlaser apparatus 1000A is referred to as a blue-violet laser beam, alaser beam having a wavelength of approximately 650 nm emitted from thered emission point 21 is referred to as a red laser beam, and a laserbeam having a wavelength of approximately 780 nm emitted from theinfrared emission point 31 is referred to as an infrared laser beam. InFIG. 15, the blue-violet laser beam and the infrared laser beam arerespectively indicated by solid lines, and the red laser beam isindicated by a dash line.

As shown in FIG. 15, the optical pickup apparatus 900 a comprises asubstantially round-shaped can package for laser devices 500 having thesemiconductor laser apparatus 1000A mounted thereon, a polarizing beamsplitter (hereinafter abbreviated as PBS) 902, a collimator lens 903, abeam expander 904, a λ/4 plate 905, an objective lens 906, a cylindricallens 907, an optical axis correction element 908, and a photodetector909.

In FIG. 15, three directions that are perpendicular to one another, asindicated by arrows X, Y, and Z, are respectively taken as anX-direction, a Y-direction, and a Z-direction.

The X-direction is a direction perpendicular to an optical recordingmedium (hereinafter referred to as an optical disk) DI serving as areproduction object. The Y-direction and the Z-direction are directionsparallel to one surface of the optical disk DI and perpendicular to eachother.

The substantially round-shaped can package for laser devices 500 havingthe semiconductor laser apparatus 1000A mounted thereon is arranged suchthat the blue-violet emission point 11, the red emission point 21, andthe infrared emission point 31 in the semiconductor laser apparatus1000A are aligned on a substantially straight line along theY-direction. As described above, the distance between the blue-violetemission point 11 and the infrared emission point 31 is significantlyshorter than the distance between the blue-violet emission point 11 andthe red emission point 21 and the distance between the infrared emissionpoint 31 and the red emission point 21. Polarization planes of the laserbeams respectively emitted from the blue-violet emission point 11, thered emission point 21, and the infrared emission point 31 are parallelto one another.

As described above, the blue-violet emission point 11 in thesemiconductor laser apparatus 1000A is positioned in a substantiallycentral portion on a Y-Z plane of the substantially round-shaped canpackage for laser devices 500.

In this example, the PBS 902, the collimator lens 903, the beam expander904, the λ/4 plate 905, and the objective lens 906 that constitute anoptical system are arranged in this order along the optical axis of ablue-violet laser beam emitted in the X-direction from the blue-violetemission point 11 (the center of the substantially round-shaped canpackage for laser devices 500). That is, the optical axis of the opticalsystem from the PBS 902 to the objective lens 906 is aligned with theoptical axis of the blue-violet laser beam.

The PBS 902 totally transmits each of the laser beams emitted from thesemiconductor laser apparatus 1000A and totally reflects the laser beamreturned from the optical disk DI.

The collimator lens 903 converts the blue-violet laser beam, the redlaser beam, or the infrared laser beam from the semiconductor laserapparatus 1000A that has been transmitted through the PBS 902 into aparallel laser beam.

The beam expander 904 comprises a concave lens, a convex lens, and anactuator (not shown).

The actuator changes the distance between the concave lens and theconvex lens depending on a servo signal from a servo circuit (notshown). This causes a wave front shape of each of the laser beamsemitted from the semiconductor laser apparatus 1000A to be corrected.

The λ/4 plate 905 converts a linearly-polarized laser beam that has beenconverted into the parallel laser beam by the collimator lens 903 into acircularly-polarized laser beam. The λ/4 plate 905 converts thecircularly-polarized laser beam returned from the optical disk DI into alinearly-polarized laser beam. The direction of polarization of thelinearly-polarized laser beam in this case is perpendicular to thedirection of polarization of the linearly-polarized laser beam emittedfrom the semiconductor laser apparatus 1000A. Thus, the laser beamreturned from the optical disk DI is almost totally reflected by the PBS902.

The objective lens 906 converges the laser beam that has beentransmitted through the λ/4 plate 905 on a surface (a recording layer)of the optical disk DI.

The objective lens 906 is movable in a focusing direction, a trackingdirection, and a tilt direction by an actuator (not shown) of theobjective lens depending on a servo signal from a servo circuit (atracking servo signal, a focusing servo signal, and a tilt servosignal).

The cylindrical lens 907, the optical axis correction element 908, andthe photodetector 909 are arranged along the optical axis of the laserbeam totally reflected by the PBS 902.

The cylindrical lens 907 applies an astigmatism to an incident laserbeam. The optical axis correction element 908 is formed by a diffractiongrating. Height of the diffraction grating is determined such thatfirst-diffracted light beams of a blue-violet semiconductor laser beamand an infrared semiconductor laser beam and a zeroth-order diffractedlight beam of a red semiconductor laser beam are weakened and such thatzeroth-order diffracted light beams of a blue-violet semiconductor laserbeam and an infrared semiconductor laser beam and a first-orderdiffracted light beam of a red semiconductor laser beam are enhanced. Ifa binary diffraction grating is used as the diffraction grating, heightof the diffraction grating is set to about 4νλ, where ν and λ are arefractive index of the diffraction grating and the wavelength of ablue-violet laser beam, respectively.

The optical axis correction element 908 introduces a blue-violet laserbeam (a zeroth-order diffracted light beam) and an infrared laser beam(a zeroth-order diffracted light beam) that have been transmittedthrough the cylindrical lens 907 into the photodetector 909.

Furthermore, the optical axis correction element 908 diffracts a redlaser beam that has been transmitted through the cylindrical lens 907,and introduces the diffracted red laser beam (a first-order diffractedlight beam) into the photodetector 909.

In this case, the optical axis correction element 908 is positioned suchthat the position of a focusing spot formed on a light detecting surfaceof the photodetector 909 by the blue-violet laser beam and the infraredlaser beam and the position of a focusing spot formed on the lightdetecting surface of the photodetector 909 by the red laser beamcoincide with each other.

The photodetector 909 outputs a reproduction signal on the basis of theintensity distribution of the received laser beam. Here, thephotodetector 909 has a detection region in a predetermined pattern suchthat a focusing error signal, a tracking error signal, and a tilt errorsignal, together with the reproduction signal, are obtained. An actuatorof the beam expander 904 and an actuator of the objective lens aresubjected to feedback control by the focusing error signal, the trackingerror signal, and the tilt error signal.

(i-1b) Effect of Optical Pickup Apparatus in First Example

As shown in FIG. 15, in the optical pickup apparatus 900 a, theblue-violet laser beam, the infrared laser beam, or the red laser beamis incident on the optical axis correction element 908 formed by thediffraction grating.

Generally, in the diffraction grating, respective diffractionefficiencies for a light beam having a certain wavelength and a lightbeam having a wavelength that is n times (n is a natural number) thewavelength can be equalized. That is, a diffraction efficiency in a casewhere the light beam having a certain wavelength is incident on thediffraction grating and a diffraction grating in a case where the lightbeam having a wavelength can be equalized. Then, because the wavelength(approximately 650 nm) of the red laser beam is not n times (n is anatural number) the wavelength (approximately 405 nm) of the blue-violetlaser beam and the wavelength (approximately 780 nm) of the infraredlaser beam, the optical axis correction element 908 allows a diffractionefficiency different from those for the blue-violet laser beam and theinfrared laser beam to be given for the red laser beam.

The distance between the blue-violet emission point 11 and the infraredemission point 31 in the Z-direction is very short. Consequently, inthis example, it can be recognized that the optical axis of theblue-violet laser beam and the optical axis of the infrared laser beamare substantially identical.

Here, the height of the diffraction grating is determined such that thefirst-order diffracted light beams of the blue-violet semiconductorlaser beam and the infrared semiconductor laser beam are weakened andsuch that the zeroth-order diffracted light beams of the blue-violetsemiconductor laser beam and the infrared semiconductor laser beam areenhanced. The optical axis correction element 908 is arranged such thatthe position of the focusing spot of the red laser beam coincides withthe position of the focusing spot of the blue-violet laser beam and theinfrared laser beam. Thus, the blue-violet laser beam, the infraredlaser beam, and the red laser beam can be received by the commonphotodetector 909.

In the optical pickup apparatus 900 a according to the presentembodiment, therefore, the photodetector 909 that is common among theblue-violet laser beam, the infrared laser beam, and the red laser beamis used. This eliminates the necessity of providing three photodetectorsrespectively corresponding to the blue-violet laser beam, the infraredlaser beam, and the red laser beam, thereby realizing miniaturization ofthe optical pickup apparatus 900 a.

In the semiconductor laser apparatus 1000A, the distance between theblue-violet emission point 11 and the infrared emission point 31 is veryshort, and the infrared emission point 31 and the red emission point 21are positioned on a straight line parallel to the Y-direction, so thatthe blue-violet emission point 11, the infrared emission point 31, andthe red emission point 21 are arranged on a substantially straight linealong the Y-direction. In a case where the semiconductor laser apparatus1000A is used for the optical pickup apparatus 900 a, therefore, theoptical pickup apparatus 900 a is easy to design.

(i-2a) Second Example of Optical Pickup Apparatus

FIG. 16 is a diagram showing another example of the configuration of anoptical pickup apparatus according to the present embodiment.

As shown in FIG. 16, the configuration of an optical pickup apparatus900 b in a second example is the same as the configuration of theoptical pickup apparatus 900 a in the first example except for thefollowing points.

That is, an optical axis correction element 908 is arranged along theoptical axis of a blue-violet laser beam emitted in the X-direction froma blue-violet emission point 11 between a substantially round-shaped canpackage for laser devices 500 and a PBS 902 instead of being providedbetween a cylindrical lens 907 and a photodetector 909.

(i-2b) Effect of Optical Pickup Apparatus in Second Example

In the above-mentioned configuration, the optical axis of a red laserbeam emitted from a red emission point 21 is aligned with the respectiveoptical axes of the blue-violet laser beam emitted from the blue-violetemission point 11 and an infrared laser beam emitted from an infraredemission point 31 by the optical axis correction element 908.

After the red laser beam is emitted from the red emission point 21,therefore, the optical axis of the red laser beam is corrected by theoptical axis correction element 908 in the first stage of an opticalsystem constructed as described above, so that the optical axis of thered laser beam is prevented from being shifted in a halfway stage of theoptical system.

On the other hand, in the optical pickup apparatus 900 b, the intensityof the red laser beam is attenuated by the optical axis correctionelement 908, as compared with that in the optical pickup apparatus 900a. However, the shift of the optical axis of the red laser beam from anobjective lens 906 can be restrained. Thus, degradation of the opticalcharacteristics of the red laser beam on the optical disk DI can berestrained.

(i-3) Third Example of Optical Pickup Apparatus and Effect ProducedThereby

FIG. 17 is a diagram showing still another example of the configurationof an optical pickup apparatus according to the present embodiment.

As shown in FIG. 17, the configuration of an optical pickup apparatus900 c in a third example is the same as the configuration of the opticalpickup apparatus 900 a in the first example except for the followingpoints.

That is, a parallel plate 911 is further provided between a PBS 902 anda cylindrical lens 907.

The provision of the parallel plate 911 eliminates the necessity ofconsidering the optical axis of a blue-violet laser beam and the opticalaxis of an infrared laser beam to be identical to each other and allowsthe optical axis of the infrared laser beam to be aligned with theoptical axis of the blue-violet laser beam, as described in the opticalpickup apparatus 900 a.

This allows both the respective optical axes of the red laser beam andthe infrared laser beam to be aligned with the optical axis of theblue-violet laser beam in this example.

In this example, the use of the parallel plate 911 without using anoptical device such as a diffraction grating allows the complexity of anoptical system to be avoided and allows the cost to be reduced.

Furthermore, in this example, the infrared laser beam aligned bycorrection is incident on a photodetector 909, so that the signalcharacteristics of the infrared laser beam are improved.

Here, the correction function of the optical axis by the parallel plate911 will be described.

FIG. 18 is a diagram for explaining the function of connecting theoptical axis of the parallel plate 911 in the optical pickup apparatus900C shown in FIG. 17.

As shown in FIG. 18, letting t be the thickness of the parallel plate911, letting t be an angle formed between a surface perpendicular to theoptical axis and a surface in a direction opposite to the thicknessdirection of the parallel plate 911 (hereinafter referred to as aninclination angle), and letting n be the refractive index of theparallel plate 911, a movement amount (a shift amount) h of the opticalaxis by the parallel plate 911 in a case where the optical axis aftercorrection (hereinafter referred to as a reference optical axis) is usedas a basis is expressed by the following equation (1):h=t/Cos(Arcsin(Sin(θ)/n))·Sin(θ)  (1)

Here, when shift amounts h1 and h2 of the blue-violet laser beam and theinfrared laser beam from the reference optical axis are calculated onthe basis of the foregoing equation (1) in a case where a refractiveindex n obtained on the basis of a glass material SF7 having an Abbe'snumber vd of 34.6 and having a reference refractive index nd of 1.64 asa material forming the parallel plate 911, for example, and thethickness t and the inclination angle θ of the parallel plate 911 arerespectively taken as 1 mm and 45°, as shown in Table 1, results asshown in Table 2 are obtained: TABLE 1 Refractive index nd vd Thicknesst [mm] Inclination angle θ [°] 1.64 34.6 1 45

TABLE 2 Blue-violet laser beam Infrared laser beam Refractive index n1.673 1.628 Shift amount [mm] h1 h2 0.780192 0.784994

From the foregoing, an amount to be corrected (hereinafter referred toas a correction amount) r represented by a difference between the shiftamount h1 of the blue-violet laser beam and the shift amount h2 of theinfrared laser beam is approximately 5 μm. Consequently, the opticalaxis of the infrared laser beam can be aligned with the optical axis ofthe blue-violet laser beam by correcting approximately 5 μm, asdescribed above, serving as the correction amount by the parallel plate911.

It is preferable that the inclination angle θ of the parallel plate 911is not more than 60°. The reason for this will be described below.

FIG. 19 is an explanatory view for explaining a preferred inclinationangle θ of the parallel plate 911.

The thickness t of the parallel plate 911 is actually not more thanapproximately 2 mm from the design relationship of the optical system.As shown in FIG. 19, the effective diameter x1 of the laser beam isgenerally not more than approximately 4 mm.

In FIG. 19, in a case where the inclination angle θ of the parallelplate 911 is 60°, the size x2 of a space occupied by the parallel plate911 in the direction of the optical axis of the laser beam is 10.97 mm.The general focal distance of the collimator lens 903 is 10 mm to 20 mm.

When the inclination angle θ of the parallel plate 911 is set to morethan 60°, therefore, it may, in some cases, be difficult to provideanother optical device or optical component between the collimator lens903 and the photodetector 909. Consequently, it is preferable that theinclination angle θ of the parallel plate 911 is not more than 60, andit is preferable that the thickness t of the parallel plate 911 is notmore than approximately 2 mm. The correction amount in this case isapproximately 21.1 μm, and is approximately 10 μm in a case where theinclination angle θ of the parallel plate 911 is 45° and the thickness tof the parallel plate 911 is 2 mm.

(i-4) Fourth Example of Optical Pickup Apparatus and Effect ProducedThereby

FIG. 20 is a diagram showing still another example of the configurationof an optical pickup apparatus according to the present embodiment.

As shown in FIG. 20, the configuration of an optical pickup apparatus900 d in a fourth example is the same as the configuration of theoptical pickup apparatus 900 b in the second example except for thefollowing points.

That is, in the optical pickup apparatus 900 d, a collimator lens 903 isprovided between an optical axis correction element 908 and a PBS 902instead of being provided between the PBS 902 and a beam expander 904.

A parallel plate 911 is provided between the PBS 902 and the collimatorlens 903 provided between the optical axis correction element 908 andthe PBS 902.

In this example, the optical axis of a red laser beam is aligned withthe optical axis of a blue-violet laser beam by the optical axiscorrection element 908, and the optical axis of an infrared laser beamis aligned with the optical axis of the blue-violet laser beam by theparallel plate 911. Thus, the optical pickup apparatus 900 d differsfrom the optical pickup apparatus 900 b in the second example, describedabove, in that the infrared laser beam aligned by correction is incidenton an objective lens 906. Thus, the optical characteristics of theinfrared laser beam on an optical disk DI can be improved, as comparedwith those in the optical pickup apparatus 900 b.

Furthermore, in this example, the infrared laser beam aligned bycorrection is incident on a photodetector 909, so that the signalcharacteristics of the infrared laser beam are improved.

Furthermore, in this example, the collimator lens 903 is providedbetween the PBS 902 and the beam expander 904, so that it is possible toprevent aberration (astigmatism) in a case where a diffused light beamor a converged light beam is incident on the parallel plate 911.

(j) Another Example of Configuration of Optical Pickup Apparatus

An optical axis correction element 908 and a parallel plate 911 may beprovided in an optical system from a PBS 902 to an objective lens 906.

In the optical pickup apparatuses 900 a to 900 d, a focusing errorsignal is generated using an astigmatism method. Further, a trackingerror signal is generated using differential phase detection (DPD), forexample.

(2) Second Embodiment

A semiconductor laser apparatus according to a second embodiment has thesame configuration as the semiconductor laser apparatus 1000A accordingto the first embodiment except for the following points.

FIG. 21 is a schematic top view for explaining the configuration of asemiconductor laser apparatus 1000B according to the second embodiment.

As shown in FIG. 21, the semiconductor laser apparatus 1000B accordingto the present embodiment comprises a blue-violet semiconductor laserdevice 1 and a monolithic red/infrared semiconductor laser device 23X.

The monolithic red/infrared semiconductor laser device 23X comprises ared semiconductor laser device 2 and an infrared semiconductor laserdevice 3, and is joined to the blue-violet semiconductor laser device 1.

The length in the X-direction of the monolithic red/infraredsemiconductor laser device 23X is larger than the length in theX-direction of the blue-violet semiconductor laser device 1.

In the present embodiment, the cavity length of the blue-violetsemiconductor laser device 1 extending in the X-direction isapproximately 600 μm, and the cavity length of the red semiconductorlaser device 2 and the infrared semiconductor laser device 3 extendingin the X-direction is 1200 μm, for example.

Here, in the present embodiment, respective laser beam emission facetsof the blue-violet semiconductor laser device 1, the red semiconductorlaser device 2, and the infrared semiconductor laser device 3 almostcoincide with one another, as shown in FIG. 21. In this case, a portionthat is not joined to the blue-violet semiconductor laser device 1occurs on the opposite side of a laser beam emission facet of themonolithic red/infrared semiconductor laser device 23X. Thus, distortionat a facet on the opposite side of the laser beam emission facets of thered semiconductor laser device 2 and the infrared semiconductor laserdevice 3 is reduced. Consequently, degradation of the red semiconductorlaser device 2 and the infrared semiconductor laser device 3 arerestrained.

Thus, the respective cavity lengths of the semiconductor laser devicesare individually adjusted, so that the reliability of each of thesemiconductor laser devices can be improved.

(3) Third Embodiment

(a) Configuration and Effect of Semiconductor Laser Apparatus

A semiconductor laser apparatus 1000C according to a third embodimenthas the same configuration as the semiconductor laser apparatus 1000Aaccording to the first embodiment except for the following points.

FIG. 22 is a top view showing an example of the semiconductor laserapparatus according to the third embodiment. FIGS. 23 and 24 areschematic views of a junction plane of a blue-violet semiconductor laserdevice 1 and a monolithic red/infrared semiconductor laser device 23X inthe semiconductor laser apparatus 1000C shown in FIG. 22. Thesemiconductor laser apparatus 1000C according to the present embodimenthas a blue-violet semiconductor laser device 1 and a monolithicred/infrared semiconductor laser device 23X similar to those shown inand 2. A cross-sectional view taken along a line A2-A2 shown in FIG. 22is identical to the cross-sectional view taken along the line A1-A1shown in FIG. 1 (see FIG. 2).

In the semiconductor laser apparatus 1000C according to the presentembodiment, a p-side pad electrode 12 and a p-side pad electrode 13 areformed on an insulating film 4 a in the blue-violet semiconductor laserdevice 1, as shown in FIG. 23 (a).

The p-side pad electrode 12 extends in the X-direction along aprojection T1 in the blue-violet semiconductor laser device 1, and itspart extends in the Y-direction.

The p-side pad electrode 13 extends in the X-direction at a positionspaced apart from the p-side pad electrode 12, and its part extends inthe opposite direction to the p-side pad electrode 12. A wire fordriving a red semiconductor laser device 2 is bonded to one end of thep-side pad electrode 13 extending in the Y-direction. The p-side padelectrode 13 extends by approximately 100 μm in width and approximately100 μm in length in the Y-direction.

The p-side pad electrodes 12 and 13 are formed so as to be spaced apartfrom each other on the insulating film 4 a. Thus, the p-side padelectrodes 12 and 13 are electrically isolated from each other.

As shown in FIG. 23 (b), an insulating film 4 b having a predeterminedwidth is formed on the insulating film 4 a and the p-side pad electrode12. The insulating film 4 b is formed such that one end of the p-sidepad electrode 12 extending in the Y-direction is exposed. A wire fordriving the blue-violet semiconductor laser device 1 is bonded to theexposed one end of the p-side pad electrode 12. A region having a widthof approximately 100 μm and having a length of approximately 100 μm atthe one end of the p-side pad electrode 12 extending in the Y-directionis exposed.

As shown in FIG. 24 (c), a p-side pad electrode 14 is formed at aposition spaced apart from the p-side pad electrode 13 on the insulatingfilm 4 a and the insulating film 4 b. The p-side pad electrode 14extends in the X-direction on the insulating film 4 a and the insulatingfilm 4 b, and its part extends in the Y-direction, similarly to thep-side pad electrode 12. Here, a portion extending in the Y-direction ofthe p-side pad electrode 12 and a portion extending in the Y-directionof the p-side pad electrode 14 are spaced apart from each other, so thatthe p-side pad electrodes 12, 13, and 14 are electrically isolated fromone another. The p-side pad electrode 14 extends by approximately 100 μmin width and approximately 100 μm in length in the Y-direction.

A wire for driving an infrared semiconductor laser device 3 is bonded toone end of the p-side pad electrode 14 extending in the Y-direction.

A solder film H composed of Au—Sn is formed on each of the p-side padelectrode 13 and the p-side pad electrode 14.

The monolithic red/infrared semiconductor laser device 23X is joined tothe blue-violet semiconductor laser device 1 (see FIG. 2) such that ap-side pad electrode 22 in the red semiconductor laser device 2 isjoined to the p-side pad electrode 13 with the solder film H sandwichedtherebetween and a p-side pad electrode 32 in the infrared semiconductorlaser device 3 is joined to the p-side pad electrode 14 with the solderfilm H sandwiched therebetween.

Thus, the p-side pad electrode 22 in the red semiconductor laser device2 is electrically connected to the p-side pad electrode 13, and thep-side pad electrode 32 in the infrared semiconductor laser device 3 iselectrically connected to the p-side pad electrode 14.

As described in the foregoing, in the semiconductor laser apparatus1000C according to the present embodiment, respective one ends of thep-side pad electrodes 12 and 14 are exposed, projecting from a sidesurface of the infrared semiconductor laser device 3 in the Y-direction.Thus, the exposed portions of the p-side pad electrodes 12 and 14extending in the Y-direction are arranged on a substantially straightline in the X-direction, so that an arrangement space of the redsemiconductor laser device 2 and the infrared semiconductor laser device3 on the blue-violet semiconductor laser device 1 in the Y-direction canbe increased. Consequently, the respective widths of the redsemiconductor laser device 2 and the infrared semiconductor laser device3 in the Y-direction can be increased.

The p-side pad electrodes 12 and 13 can be simultaneously formed, sothat the manufacturing processes can be simplified.

The third embodiment differs from the first embodiment in that thep-side pad electrode 14 is not formed on the p-side pad electrode 13.Therefore, the necessity of forming the solder film H on the p-side padelectrode 13 is eliminated, so that the manufacturing processes can besimplified.

(b) State Where Semiconductor Laser Apparatus is Mounted on Package forLaser Devices

FIG. 25 is a schematic front view showing a state where thesemiconductor laser apparatus 1000C shown in FIG. 22 is mounted withinthe substantially round-shaped can package for laser devices 500 shownin FIG. 5 to remove the cover 504, and FIG. 26 is a schematic top viewshowing a state where the semiconductor laser apparatus 1000C shown inFIG. 22 is mounted within the substantially round-shaped can package forlaser devices 500 shown in FIG. 5 to remove the cover 504. In FIGS. 25and 26, an X-direction, a Y-direction, and a Z-direction are alsodefined, as in FIG. 1.

As shown in FIGS. 25 and 26, a power feed pin 501 a is connected to oneend of the p-side pad electrode 13 in the semiconductor laser apparatus1000C through a wire W1. A power feed pin 501 b is connected to one endof the p-side pad electrode 14 in the semiconductor laser apparatus1000C through a wire W2. A power feed pin 501 c is connected to one endof the p-side pad electrode 12 in the semiconductor laser apparatus1000C through a wire W3.

On the other hand, an exposed upper surface of a supporting member 505is electrically connected to a common n-electrode 233 in thesemiconductor laser apparatus 1000C through a wire W4.

Here, the supporting member 505 is electrically connected through asubmount 505S and an adhesion layer 505H. Thus, a power feed pin 502 iselectrically connected to an n-electrode 15 in the blue-violetsemiconductor laser device 1 and the n-electrode 233 that is commonbetween the red semiconductor laser device 2 and the infraredsemiconductor laser device 3. That is, common cathode wire connection ofthe blue-violet semiconductor laser device 1, the red semiconductorlaser device 2, and the infrared semiconductor laser device 3 isimplemented.

The blue-violet semiconductor laser device 1 can be driven by applying avoltage between the power feed pin 501 c and the power feed pin 502. Thered semiconductor laser device 2 can be driven by applying a voltagebetween the power feed pin 501 a and the power feed pin 502. Theinfrared semiconductor laser device 3 can be driven by applying avoltage between the power feed pin 501 b and the power feed pin 502. Theblue-violet semiconductor laser device 1, the red semiconductor laserdevice 2, and the infrared semiconductor laser device 3 can be thusindependently driven.

In the semiconductor laser apparatus 1000C according to the presentembodiment, the p-side pad electrodes 12, 13, and 14 are electricallyisolated from one another, as described above. Thus, arbitrary voltagescan be respectively applied to the p-side pad electrodes 12, 13, and 14in the blue-violet semiconductor laser device 1, the red semiconductorlaser device 2, and the infrared semiconductor laser device 3.Consequently, a system for driving the blue-violet semiconductor laserdevice 1, the red semiconductor laser device 2, and the infraredsemiconductor laser device 3 can be arbitrary selected.

(c) Effect in State Where Semiconductor Laser Apparatus is Mounted onPackage for Laser Devices

In the present embodiment, the semiconductor laser apparatus 1000C isalso made to adhere to the submount 505S such that a blue-violetemission point 11 in the blue-violet semiconductor laser device 1 ispositioned at the center of the extraction window 504 a in the cover 504(see FIG. 5). Further, the blue-violet emission point 11 and an infraredemission point 31 are provided at positions in close proximity to eachother. In the present embodiment, therefore, the same effect as that inthe first embodiment can be obtained.

As shown in FIGS. 25 and 26, the exposed portion of the p-side padelectrode 12 in the blue-violet semiconductor laser device 1 is providedso as to be positioned farther apart from a laser beam emission facet ofthe semiconductor laser apparatus 1000C than the exposed portion of thep-side pad electrode 14 in the infrared semiconductor laser device 3.Therefore, the p-side pad electrode 12 can be easily connected to thepower feed pin 501 c opposed to a surface, on which a semiconductorlaser apparatus is mounted, of the supporting member 505, and the lengthof the wire W3 can be shortened.

Although in this example, the exposed portion of the p-side padelectrode 14 in the infrared semiconductor laser device 3 is arranged onthe side of the laser beam emission facet of the semiconductor laserapparatus 1000C in the X-direction, the p-side pad electrode 12 in theblue-violet semiconductor laser device 1 may be arranged on the side ofthe laser beam emission facet of the semiconductor laser apparatus1000C. In this case, the p-side pad electrode 12 in the blue-violetsemiconductor laser device 1 and the power feed pin 501 b are connectedto each other through a wire. The p-side pad electrode 14 in theinfrared semiconductor laser device 3 and the power feed pin 501 c areconnected to each other through a wire.

(4) Fourth Embodiment

(a) Configuration of Semiconductor Laser Apparatus

FIGS. 27 and 28 are schematic views for explaining the configuration ofa semiconductor laser apparatus according to a fourth embodiment. FIG.27 is a top view showing an example of the semiconductor laser apparatusaccording to the fourth embodiment, and FIG. 28 is a cross-sectionalview taken along a line A3-A3 shown in FIG. 27. FIGS. 29 and 30 areschematic views of respective junction planes among a blue-violetsemiconductor laser device 1, a red semiconductor laser device 2, and aninfrared semiconductor laser device 3 in the semiconductor laserapparatus shown in FIGS. 27 and 28.

In FIGS. 27 to 30, an X-direction, a Y-direction, and a Z-direction arealso defined, as in FIG. 1.

As shown in FIGS. 27 and 28, in a semiconductor laser apparatus 1000Daccording to the present embodiment, a monolithic red/infraredsemiconductor laser device 23Y having the red semiconductor laser device2 and the infrared semiconductor laser device 3 integrally formedtherein is jointed to the blue-violet semiconductor laser device 1.

Here, the monolithic red/infrared semiconductor laser device 23Y shownin FIGS. 27 and 28 has a different configuration from the monolithicred/infrared semiconductor laser device 23X shown in FIGS. 1 and 2. Inthe monolithic red/infrared semiconductor laser device 23Y shown inFIGS. 27 and 28, a hole QH is formed between the red semiconductor laserdevice 2 and the infrared semiconductor laser device 3. One end of ap-side pad electrode 14, described later, is exposed to the exteriorthrough the hole QH.

In the present embodiment, the infrared semiconductor laser device 3 isjoined to the blue-violet semiconductor laser device 1 such that aprojection T1 in the blue-violet semiconductor laser device 1 and aprojection T3 in the infrared semiconductor laser device 3 are opposedto each other on a substantially straight line in the Z-direction, as inthe semiconductor laser apparatus 1000A shown in FIGS. 1 and 2. That is,a blue-violet emission point 11 and an infrared emission point 31 arerespectively provided at positions in close proximity to each other.

A junction of the blue-violet semiconductor laser device 1 and themonolithic red/infrared semiconductor laser device 23Y will bedescribed.

As shown in FIG. 29 (a), a p-side pad electrode 12 extends in theX-direction along the projection T1 in the blue-violet semiconductorlaser device 1, and its part extends in the Y-direction.

A p-side pad electrode 13 extends in the X-direction at a positionspaced apart from the p-side pad electrode 12, and its part extends inthe opposite direction to the p-side pad electrode 12. A wire fordriving the red semiconductor laser device 2 is bonded to one end of thep-side pad electrode 13 extending in the Y-direction. The p-side padelectrode 12 extends by approximately 100 μm in width and approximately100 μm in length in the Y-direction.

Since the p-side pad electrodes 12 and 13 are formed so as to be spacedapart from each other on an insulating film 4 a, the p-side padelectrodes 12 and 13 are electrically isolated from each other.

As shown in FIG. 29 (b), an insulating film 4 b having a predeterminedwidth is formed on the insulating film 4 a and the p-side pad electrode12. The insulating film 4 b is formed such that one end of the p-sidepad electrode 12 extending in the Y-direction is exposed. A wire fordriving the blue-violet semiconductor laser device 1 is bonded to theexposed one end of the p-side pad electrode 12. A region having a widthof approximately 100 μm and having a length of approximately 100 μm atthe one end of the p-side pad electrode 12 extending in the Y-directionis exposed.

As shown in FIG. 30 (c), the p-side pad electrode 14 is formed at aposition spaced apart from the p-side pad electrode 13 on the insulatingfilm 4 a and the insulating film 4 b. The p-side pad electrode 14extends in the X-direction on the insulating film 4 a and the insulatingfilm 4 b, and its part extends in the opposite direction on asubstantially straight line to a portion extending in the Y-direction ofthe p-side pad electrode 12. The p-side pad electrode 12 extends byapproximately 100 μm in width and approximately 100 μm in length in theY-direction. A portion extending in the Y-direction of the p-side padelectrode 14 is spaced apart from the p-side pad electrode 13.Consequently, the p-side pad electrodes 12, 13, and 14 are electricallyisolated from one another.

A wire for driving the infrared semiconductor laser device 3 is bondedto one end of the p-side pad electrode 14 extending in the Y-directionthrough the hole QH.

A solder film H composed of Au—Sn is formed on each of the p-side padelectrode 13 and the p-side pad electrode 14.

The monolithic red/infrared semiconductor laser device 23Y is joined tothe blue-violet semiconductor laser device 1 such that a p-side padelectrode 22 in the red semiconductor laser device 2 is joined to thep-side pad electrode 13 with the solder film H sandwiched therebetweenand a p-side pad electrode 32 in the infrared semiconductor laser device3 is joined to the p-side pad electrode 14 with the solder film Hsandwiched therebetween.

Thus, the p-side pad electrode 22 in the red semiconductor laser device2 is electrically connected to the p-side pad electrode 13, and thep-side pad electrode 32 in the infrared semiconductor laser device 3 iselectrically connected to the p-side pad electrode 14.

As described in the foregoing, in the semiconductor laser apparatus1000D according to the present embodiment, the p-side pad electrodes 12and 13 can be simultaneously formed, so that the manufacturing processescan be simplified.

The solder film H need not be formed on the p-side pad electrodes 13, sothat the manufacturing processes can be simplified.

In the present embodiment, the distance between a red emission point 21and an infrared emission point 31 in the Y-direction is adjusted toapproximately 200 μm, for example.

The width of the blue-violet semiconductor laser device 1 in theY-direction is approximately 800 μm, for example. The width of themonolithic red/infrared semiconductor laser device 23Y in theY-direction is approximately 400 μm, for example.

It is preferable that the respective diameters of the blue-violetemission point 11 and the infrared emission point 31 are not more than20 μm.

(b) State Where Semiconductor Laser Apparatus is Mounted on Package forLaser Devices

FIG. 31 is a schematic front view showing a state where thesemiconductor laser apparatus 1000D shown in FIGS. 27 and 28 is mountedwithin the substantially round-shaped can package for laser devices 500shown in FIG. 5 to remove the cover 504. In FIG. 31, the semiconductorlaser apparatus 1000D provided in the substantially round-shaped canpackage for laser devices 500 is indicated by a cross section takenalong a line A3-A3 shown in FIG. 27. In FIG. 31, an X-direction, aY-direction, and a Z-direction are also defined, as in FIG. 1.

As shown in FIG. 31, a power feed pin 501 a is connected to one end ofthe p-side pad electrode 13 in the semiconductor laser apparatus 1000Dthrough a wire W1. A power feed pin 501 b is connected to one end of thep-side pad electrode 12 in the semiconductor laser apparatus 1000Dthrough a wire W2. A power feed pin 501 c is connected to one end of thep-side pad electrode 14 in the semiconductor laser apparatus 1000Dthrough a wire w3.

On the other hand, an exposed upper surface of a supporting member 505and a common n-electrode 233 in the semiconductor laser apparatus 1000Dare electrically connected to each other through a wire W4.

Here, the supporting member 505 is electrically connected through asubmount 505S and an adhesion layer 505H. Thus, a power feed pin 502 iselectrically connected to an n-electrode 15 in the blue-violetsemiconductor laser device 1 and an n-electrode 233 that is commonbetween the red semiconductor laser device 2 and the infraredsemiconductor laser device 3. That is, common cathode wire connection ofthe blue-violet semiconductor laser device 1, the red semiconductorlaser device 2, and the infrared semiconductor laser device 3 isimplemented.

The blue-violet semiconductor laser device 1 can be driven by applying avoltage between the power feed pin 501 b and the power feed pin 502. Thered semiconductor laser device 2 can be driven by applying a voltagebetween the power feed pin 501 a and the power feed pin 502. Theinfrared semiconductor laser device 3 can be driven by applying avoltage between the power feed pin 501 c and the power feed pin 502. Theblue-violet semiconductor laser device 1, the red semiconductor laserdevice 2, and the infrared semiconductor laser device 3 can be thusindependently driven.

In the semiconductor laser apparatus 1000D according to the presentembodiment, the p-side pad electrodes 12, 13, and 14 are electricallyisolated from one another, as described above. Thus, arbitrary voltagescan be respectively applied to the p-side pad electrodes 12, 13, and 14in the blue-violet semiconductor laser device 1, the red semiconductorlaser device 2, and the infrared semiconductor laser device 3.Consequently, a system for driving the blue-violet semiconductor laserdevice 1, the red semiconductor laser device 2, and the infraredsemiconductor laser device 3 can be arbitrary selected.

(c) Effect in State Where Semiconductor Laser Apparatus is Mounted onPackage for Laser Devices

In the present embodiment, the semiconductor laser apparatus 1000D isalso made to adhere to the submount 505S such that the blue-violetemission point 11 in the blue-violet semiconductor laser device 1 ispositioned at the center of the extraction window 504 a in the cover 504(see FIG. 5). Further, the blue-violet emission point 11 and an infraredemission point 31 are provided at positions in close proximity to eachother. In the present embodiment, therefore, the same effect as that inthe first embodiment can be also obtained.

The p-side pad electrode 14 in the infrared semiconductor laser device 3is exposed to the exterior through a hole QH. Thus, it is possible tobond a wire to the p-side pad electrodes 14 through the hole QH. As aresult, the degree of freedom of wiring is improved.

The p-side pad electrodes 12, 13, and 14 can be provided on the oppositeside of a light emission surface. Thus, the length of the wire can beshortened in respectively connecting the p-side pad electrode 12, 13,and 14 to the power feed pins 501 b, 501 a, and 501 c. Consequently, theresponse characteristics of the blue-violet semiconductor laser device1, the red semiconductor laser device 2, and the infrared semiconductorlaser device 3 can be improved.

(5) Fifth Embodiment

(a) Configuration of Semiconductor Laser Apparatus

FIGS. 32 and 33 are schematic views for explaining the configuration ofa semiconductor laser apparatus 1000E according to a fifth embodiment.FIG. 32 is a top view showing an example of the semiconductor laserapparatus according to the fifth embodiment, and FIG. 33 is across-sectional view taken along a line A4-A4 shown in FIG. 32. In FIGS.32 and 33, an X-direction, a Y-direction, and a Z-direction are alsodefined, as in FIG. 1.

Also in the present embodiment, an infrared semiconductor laser device 3is joined to a blue-violet semiconductor laser device 1 such that aprojection T1 in the blue-violet semiconductor laser device 1 and aprojection T3 in the infrared semiconductor laser device 3 are opposedto each other on a substantially straight line in the Z-direction, as inthe semiconductor laser apparatus 1000A shown in FIGS. 1 and 2. That is,a blue-violet emission point 11 and an infrared emission point 31 areprovided at positions in close proximity to each other.

As shown in FIGS. 32 and 33, the blue-violet semiconductor laser device1 in the semiconductor laser apparatus 1000E according to the presentembodiment, a p-side pad electrode 12 is formed so as to cover the wholeof respective upper surfaces of a p-type ohmic electrode 621 and aninsulating film 4 a. A solder film H is formed in a predetermined regionon the p-side pad electrode 12. Further, a monolithic red/infraredsemiconductor laser device 23Z having the red semiconductor laser device2 and the infrared semiconductor laser device 3 integrally formedtherein is jointed on the solder film H.

Here, the monolithic red/infrared semiconductor laser device 23Z shownin FIGS. 32 and 33 has a different configuration from the monolithicred/infrared semiconductor laser device 23X shown in FIGS. 1 and 2. Inthe monolithic red/infrared semiconductor laser device 23Z according tothe present embodiment, a semiconductor layer 2 t in the redsemiconductor laser device 2 (see FIG. 13) and a semiconductor layer 3 tin the infrared semiconductor laser device 3 (see FIG. 14) are connectedto each other by a connecting portion BR.

The connecting portion BR may include a part of the semiconductor layer2 t in the red semiconductor laser device 2 or the semiconductor layer 3t in the infrared semiconductor laser device 3. For example, theconnecting portion BR may be a current blocking layer for limiting theflow of a current in the red semiconductor laser device 2 and theinfrared semiconductor laser device 3 or may be a p-type contact layer.

Thus, the semiconductor layer 2 t in the red semiconductor laser device2, the semiconductor layer 3 t in the infrared semiconductor laserdevice 3, and the connecting portion BR respectively have continuousplanes. In the monolithic red/infrared semiconductor laser device 23Z, acommon p-side pad electrode 232 is formed on the continuous planes.

The common p-side pad electrode 232 in the monolithic red/infraredsemiconductor laser device 23Z is joined to the solder film H on theblue-violet semiconductor laser device 1. Here, the blue-violetsemiconductor laser device 1 and the monolithic red/infraredsemiconductor laser device 23Z are joined to each other such that theprojection T1 in the blue-violet semiconductor laser device 1 and theprojection T3 in the infrared semiconductor laser device 3 are opposedto each other on a substantially straight line in the Z-direction, as inthe semiconductor laser apparatus 1000A shown in FIGS. 1 and 2.

In the red semiconductor laser device 2 in the monolithic red/infraredsemiconductor laser device 23Z, an n-electrode 23 is formed on a surfaceon the opposite side of the common p-side pad electrode 232. In theinfrared semiconductor laser device 3, an n-electrode 33 is formed on asurface on the opposite side of the common p-side pad electrode 232.

In the present embodiment, the distance between a red emission point 21and the infrared emission point 31 in the Y-direction is adjusted toapproximately 40 μm, for example.

The width of the blue-violet semiconductor laser device 1 in theY-direction is approximately 400 μm, for example. The width of themonolithic red/infrared semiconductor laser device 23Y in theY-direction is approximately 200 μm, for example.

(b) State Where Semiconductor Laser Apparatus is Mounted on Package forLaser Devices

FIG. 34 is a schematic front view showing a state where thesemiconductor laser apparatus 1000E shown in FIGS. 32 and 33 is mountedwithin the substantially round-shaped can package for laser devices 500shown in FIG. 5 to remove the cover 504. In FIG. 34, the semiconductorlaser apparatus 1000E provided in the substantially round-shaped canpackage for laser devices 500 is indicated by a cross section takenalong a line A4-A4 shown in FIG. 32. In FIG. 34, an X-direction, aY-direction, and a Z-direction are also defined, as in FIGS. 1 and 2.

In the present embodiment, a submount 505S having insulating propertiesis formed on a supporting member 505 in the substantially round-shapedcan package for laser devices 500.

As shown in FIG. 34, the semiconductor laser apparatus 1000E is made toadhere on the submount 505S having insulating properties with anadhesion layer 505H sandwiched therebetween.

A power feed pin 501 a is connected to an n-electrode 23 in thesemiconductor laser apparatus 1000E (the n-electrode 23 in the redsemiconductor laser device 2) through a wire W1. A power feed pin 501 bis connected to the adhesion layer 505H exposed on the submount 505Sthrough a wire W2. A power feed pin 501 c is connected to an n-electrode33 in the semiconductor laser apparatus 1000E (the n-electrode 33 in theinfrared semiconductor laser device 3) through a wire W3.

On the other hand, the p-side pad electrode 12 exposed on theblue-violet semiconductor laser device 1 and the supporting member 505are electrically connected to each other through a wire W4.

Here, the p-side pad electrode 12 on the blue-violet semiconductor laserdevice 1 is electrically connected to the common p-side pad electrode232 in the monolithic red/infrared semiconductor laser device 23Z. Thus,common anode wire connection of the blue-violet semiconductor laserdevice 1, the red semiconductor laser device 2, and the infraredsemiconductor laser device 3 is implemented.

The red semiconductor laser device 2 can be driven by applying a voltagebetween the power feed pin 501 a and a power feed pin 502. Theblue-violet semiconductor laser device 1 can be driven by applying avoltage between the power feed pin 501 b and the power feed pin 502. Theinfrared semiconductor laser device 3 can be driven by applying avoltage between the power feed pin 501 c and the power feed pin 502. Theblue-violet semiconductor laser device 1, the red semiconductor laserdevice 2, and the infrared semiconductor laser device 3 can be thusindependently driven.

(c) Effect in State Where Semiconductor Laser Apparatus is Mounted onPackage for Laser Devices

In the present embodiment, the semiconductor laser apparatus 1000E isalso made to adhere to the submount 505S such that the blue-violetemission point 11 in the blue-violet semiconductor laser device 1 ispositioned at the center of the extraction window 504 a in the cover 504(see FIG. 5). Further, the blue-violet emission point 11 and theinfrared emission point 31 are provided at positions in close proximityto each other. In the present embodiment, therefore, the same effect asthat in the first embodiment can be also obtained.

In the present embodiment, when the semiconductor laser apparatus 1000Eis mounted on the substantially round-shaped can package for laserdevices 500, the power feed pins 501 a to 501 c are respectivelyconnected to the n-electrodes 23 and 33 exposed on the top of thesemiconductor laser apparatus 1000E and the exposed adhesion layer 505Hby the wires W1, W3, and W2. This makes it easy to connect the wires W1to W3 with respect to the semiconductor laser apparatus 1000E.

In the present embodiment, chips of the blue-violet semiconductor laserdevice 1 and chips of the monolithic red/infrared semiconductor laserdevice 23Z may be previously individually formed, and the chips may beaffixed to one another to manufacture the semiconductor laser apparatus1000E.

(6) Correspondence to Claims

In the following paragraphs, non-limiting examples of correspondencesbetween various elements recited in the claims below and those describedabove with respect to various preferred embodiments of the presentinvention are explained. In the embodiments described above, theX-direction corresponds to a first direction, the laser beam having awavelength of 405 nm and the blue-violet laser beam correspond to alight beam having a first wavelength, the blue-violet emission point 11corresponds to a first emission point, the blue-violet semiconductorlaser device 1 corresponds to a first semiconductor laser device, thelaser beam having a wavelength of approximately 650 nm and the red laserbeam correspond to a light beam having a second wavelength, the redemission point 21 corresponds to a second emission point, the redsemiconductor laser device 2 corresponds to a second semiconductor laserdevice, the laser beam having a wavelength of approximately 780 nm andthe infrared laser beam correspond to a light beam having a thirdwavelength, the infrared emission point 31 corresponds to a thirdemission point, the infrared semiconductor laser device 3 corresponds toa third semiconductor laser device, and the Y-Z plane corresponds to afirst surface perpendicular to the first direction.

Furthermore, the semiconductor layer it corresponds to a firstsemiconductor layer, the p-side pad electrode 12 corresponds to a firstelectrode, the semiconductor layer 2 t corresponds to a secondsemiconductor layer, the p-side pad electrode 22 corresponds to a secondelectrode, the semiconductor layer 3 t corresponds to a thirdsemiconductor layer, the p-side pad electrode 32 corresponds to a thirdelectrode, the n-GaN substrate is corresponds to a first substrate, then-GaAs substrate 50 and the n-GaAs substrate 5X correspond to a secondor third substrate, the projection T1 corresponds to a first projection,the projection T2 corresponds to a second projection, the projection T3corresponds to a third projection, the Y-direction corresponds to asecond direction, and the substantially round-shaped can package forlaser devices 500 corresponds to a package.

Furthermore, the optical disk DI corresponds to an optical recordingmedium, the PBS 902, the collimator lens 903, the beam expander 904, theλ/4 plate 905, the objective lens 906, the cylindrical lens 907, and theoptical axis correction element 908 correspond to an optical system, andthe optical axis correction element 908 corresponds to a diffractiongrating.

(7) Another Embodiment

Although in the first to fifth embodiments described above, the examplein which the semiconductor laser apparatus is mounted on thesubstantially round-shaped can package for laser devices wasillustrated, the present invention is not limited to the same. Forexample, the present invention is also applicable to a case where thesemiconductor laser apparatus is mounted on another package such as aframe-type package for laser devices.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A semiconductor laser apparatus comprising: a first semiconductorlaser device, a second semiconductor laser device, and a thirdsemiconductor laser device, said first semiconductor laser devicecomprising a first semiconductor layer having a first emission pointemitting a light beam having a first wavelength in a directionsubstantially parallel to a first direction on a first substrate, saidsecond semiconductor laser device comprising a second semiconductorlayer having a second emission point emitting a light beam having asecond wavelength different from a natural number times said firstwavelength in the direction substantially parallel to the firstdirection, said third semiconductor laser device comprising a thirdsemiconductor layer having a third emission point emitting a light beamhaving a third wavelength substantially equal to a natural number timessaid first wavelength in the direction substantially parallel to thefirst direction, said second semiconductor laser device and said thirdsemiconductor laser device being stacked on said first semiconductorlaser device such that said second semiconductor layer and said thirdsemiconductor layer are opposed to said first semiconductor layer, andthe distance between said first emission point and said third emissionpoint being shorter than the distance between said first emission pointand said second emission point on a first plane perpendicular to saidfirst direction.
 2. The semiconductor laser apparatus according to claim1, wherein said first and third emission points are arranged along adirection substantially perpendicular to one surface of said firstsubstrate.
 3. The semiconductor laser apparatus according to claim 1,wherein said first semiconductor layer comprises a first cavityextending in the direction substantially parallel to said firstdirection, said second semiconductor layer comprises a second cavityextending in the direction substantially parallel to said firstdirection, said third semiconductor layer comprises a third cavityextending in the direction substantially parallel to said firstdirection, and at least one of the length of said second cavity and thelength of the third cavity is larger than the length of said firstcavity.
 4. The semiconductor laser apparatus according to claim 1,wherein said first semiconductor laser device further comprises a firstelectrode formed on said first semiconductor layer, said secondsemiconductor laser device further comprises a second electrode formedon said second semiconductor layer, said third semiconductor laserdevice further comprises a third electrode formed on said thirdsemiconductor layer, and said first electrode, said second electrode,and said third electrode are insulated from one another.
 5. Thesemiconductor laser apparatus according to claim 1, wherein said secondsemiconductor laser device further comprises a second substrate, saidsecond semiconductor layer being formed on said second substrate, saidthird semiconductor laser device further comprises a third substrate,said third semiconductor layer being formed on said third substrate, andat least one of said second substrate and said third substrate beingcomposed of a material different from said first substrate.
 6. Thesemiconductor laser apparatus according to claim 5, wherein said secondand third substrates are a common substrate, and said secondsemiconductor layer is formed in a first region of said commonsubstrate, and said third semiconductor layer is formed in a secondregion of said common substrate.
 7. The semiconductor laser apparatusaccording to claim 6, wherein a thickness from said common substrate toa surface of said second semiconductor layer is larger than a thicknessfrom said common substrate to a surface of said third semiconductorlayer in a direction substantially perpendicular to one surface of saidfirst substrate.
 8. The semiconductor laser apparatus according to claim6, wherein the surface of said second semiconductor layer projectstoward said first substrate farther than the surface of said thirdsemiconductor layer in the direction substantially perpendicular to onesurface of said first substrate.
 9. The semiconductor laser apparatusaccording to claim 1, wherein said first semiconductor layer comprises afirst projection extending in the direction substantially parallel tosaid first direction, said third semiconductor layer comprises a thirdprojection extending in the direction substantially parallel to saidfirst direction, and the width of said third projection is larger thanthe width of said first projection in a second direction perpendicularto said first direction and parallel to one surface of the firstsubstrate.
 10. The semiconductor laser apparatus according to claim 9,wherein said second semiconductor layer comprises a second projectionextending in the direction substantially parallel to said firstdirection, and the width of said third projection is larger than thewidth of said second projection in said second direction.
 11. Thesemiconductor laser apparatus according to claim 1, further comprising apackage accommodating said first semiconductor laser device, said secondsemiconductor laser device, and said third semiconductor laser device aswell as having a light extraction window, said first semiconductor laserdevice being arranged such that a light beam having a first wavelengthemitted from said first emission point in said first semiconductor laserdevice passes through a substantially central portion of said extractionwindow.
 12. The semiconductor laser apparatus according to claim 1,wherein the light beam having said first wavelength is a blue-violetlight beam, the light beam having said second wavelength is a red lightbeam, and the light beam having said third wavelength is an infraredlight beam.
 13. The semiconductor laser apparatus according to claim 1,wherein said first semiconductor layer is composed of a nitride basedsemiconductor.
 14. The semiconductor laser apparatus according to claim1, wherein said second semiconductor layer is composed of a galliumindium phosphide based semiconductor.
 15. The semiconductor laserapparatus according to claim 1, wherein said third semiconductor layeris composed of a gallium arsenide based semiconductor.
 16. An opticalpickup apparatus that irradiates a light beam onto an optical recordingmedium and detects the light beam returned from the optical recordingmedium, comprising a semiconductor laser apparatus, said semiconductorlaser apparatus comprising a first semiconductor laser device, a secondsemiconductor laser device, and a third semiconductor laser device, saidfirst semiconductor laser device comprising a first semiconductor layerhaving a first emission point emitting a light beam having a firstwavelength in a direction substantially parallel to a first direction ona first substrate, said second semiconductor laser device comprising asecond semiconductor layer having a second emission point emitting alight beam having a second wavelength different from a natural numbertimes said first wavelength in the direction substantially parallel tothe first direction, said third semiconductor laser device comprising athird semiconductor layer having a third emission point emitting a lightbeam having a third wavelength substantially equal to a natural numbertimes said first wavelength in the direction substantially parallel tothe first direction, said second semiconductor laser device and saidthird semiconductor laser device being stacked on said firstsemiconductor laser device such that said second semiconductor layer andsaid third semiconductor layer are opposed to said first semiconductorlayer, and the distance between said first emission point and said thirdemission point being shorter than the distance between said firstemission point and said second emission point on a first planeperpendicular to said first direction.
 17. The optical pickup apparatusaccording to claim 16, further comprising a photodetector, and anoptical system that introduces the light beam having said first, second,or third wavelength emitted from said semiconductor laser apparatus tosaid optical recording medium and introduces the light beam having saidfirst, second, or third wavelength returned from said optical recordingmedium to said photodetector.
 18. The optical pickup apparatus accordingto claim 17, wherein said optical system comprises a diffraction gratingthat transmits the light beams respectively having said first, second,and third wavelengths such that the light beams having said first,second, and third wavelengths are introduced into said photodetector.19. A method of manufacturing a semiconductor laser apparatus,comprising the steps of: forming a first semiconductor layer having afirst emission point emitting a light beam having a first wavelength ina direction substantially parallel to a first direction on a firstsubstrate, forming a second semiconductor layer having a second emissionpoint emitting a light beam having a second wavelength different from anatural number times said first wavelength in the directionsubstantially parallel to said first direction on a second substrate anda third semiconductor layer having a third emission point emitting alight beam having a third wavelength substantially equal to a naturalnumber times said first wavelength in the direction substantiallyparallel to the first direction; and affixing one surface of said secondsemiconductor layer to one surface of said first semiconductor layersuch that the distance between said first emission point and said thirdemission point is shorter than the distance between said first emissionpoint and said second emission point on a first plane perpendicular tosaid first direction.
 20. The method according to claim 19, wherein thethickness of said second semiconductor layer is larger than thethickness of said third semiconductor layer in a direction substantiallyperpendicular to one surface of said first substrate.
 21. The methodaccording to claim 19, wherein the surface of said second semiconductorlayer projects toward said first substrate farther than a surface ofsaid third semiconductor layer in the direction substantiallyperpendicular to one surface of said first substrate.